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Green hydrogen generation: A cross-disciplinary challenge rooted in electrochemistry

Green hydrogen generation: A cross-disciplinary challenge rooted in electrochemistry

Green hydrogen, produced from water electrolysis using renewable energy sources, is being explored as a strategy to reduce the dependence on fossil fuels and decarbonize chemical processes. From an environmental standpoint, this approach is extremely attractive given that mild conditions are used during electrolysis and there are no greenhouse gases produced when using the hydrogen in a fuel cell.

However, the economics of electrolysis and fuel cell systems for energy conversion relies heavily on the costs of electricity and of metals like nickel, platinum, iridium, and titanium. Electrolyzer operating expenses must be minimized for green hydrogen to become an economically viable option. The electricity input contributes heavily to cost. Thus, decreasing the cost of renewable energy is a necessary step. Solar panels becoming more efficient and affordable within the past decades is cause for optimism in this regard [1], but there is much more that can be done to increase the success of green hydrogen. More efficient electrolyzers could make better use of the input electricity and the development of cheaper and more durable components can reduce both the capital and operational costs.

Check out our other blog articles about green hydrogen and decarbonization of chemical processes below!

Cross-disciplinary interest in green hydrogen

Electrolyzers are primarily electrochemical devices with electrocatalysts responsible for water splitting (Figure 1). The scientific challenges related to optimizing electrolyzers are attracting the attention of researchers that are not traditionally trained in electrochemistry. The search for efficient HER (Hydrogen Evolution Reaction) and OER (Oxygen Evolution Reaction) electrocatalysts also piques the interest of inorganic chemists and physicists. Development of better membranes calls for expertise in organic and polymer chemistry. Optimization of catalyst inks and their interaction with substrates requires the know-how of a materials scientist. Heat and mass flow management within the fuel cell stack and balance of plant are engineering endeavors. Clearly, the ongoing development of green hydrogen technologies has encouraged the collaboration of scientists and engineers across many disciplines. The result is an influx of creativity and insight, as well as development of exciting new materials and techniques.

Figure 1. Diagram of the electrolysis of water (water splitting) with respective half reactions at the cathode and anode in alkaline and acidic media.

Back to basics

Working in an unfamiliar domain means there is a need for quickly getting up to speed with best practices and learning a new scientific vocabulary. For many institutions, education on electrochemical principles and laboratory skills was not a key focus area until recent years.

In some cases, the deficiency of fundamental electrochemical training has led to inconsistencies in the reporting of important performance indicators. The electrochemical community has taken note of this and called for a more rigorous approach. As a result, experts have stepped up and provided practical guidance for quantifying and reporting in this domain.

When investigating electrocatalyst materials it is necessary to have benchmarks and well-defined performance indicators. In 2013, a comprehensive benchmarking protocol for evaluating and reporting figures of merit for OER electrocatalysts was published.

This JACS article [2] provides practical advice on how to interpret the catalyst surface in terms of roughness and geometric surface area and how to perform and analyze measurements for valid comparisons of electrocatalytic performance.

A common source of confusion and inconsistency in electrochemical measurements is the use of various reference electrodes (RE). Electrocatalytic activity is judged by the overpotential needed for a specified production rate (i.e., the current density for the HER or OER process, Figure 1). A three-electrode setup is needed to measure the potential, and the RE is crucial for situating this potential on a relative scale, allowing comparison of measurements carried out by different groups and in various conditions.

Find out more about reference electrodes and their usage in our free Application Note.

A 2020 Viewpoint article in ACS Energy Letters [3] provides a detailed explanation of how to report the overpotential of an electrocatalyst, focusing on commonly used reference electrodes like Hg/HgO, Hg/Hg2Cl2 (SCE), and Ag/AgCl.

The reversible hydrogen electrode (RHE) is another commonly used RE that is extremely well-suited for HER and OER studies. A recent ACS Catalysis article [4] explains why the RHE is the ideal reference electrode for electrolysis research and explains how to prepare and work with an RHE. By convention, all standard redox potentials are reported versus the standard hydrogen electrode (SHE). The RHE is a pH-dependent extension of the SHE and refers to the reduction of a proton under non-standard conditions as described by the Nernst equation.

Electrolyzers operate under both acidic and alkaline conditions, thus, the HER and OER are studied across the pH scale (Figure 1). The RHE is suitable for use at any pH and it shares the same dependency on pH as the HER and OER.

A common ground to stand on

Finding common language and understanding between these different fields is vital. This JOC synopsis article [5] clarifies electrochemical concepts for organic chemists. The article is highly visual, providing schematics that link concepts like free energy, redox potential, and overpotential. Equilibrium thermodynamics helps to provide a common point of reference that all chemists can relate to.

Thermodynamic analysis is often applied to quantify the energy efficiency of electrolysis cells and stacks. A recent review article in the Journal of Power Sources [6] highlights diverging definitions for the energy efficiency coefficient from academic and industrial literature. The article provides derivations in various conditions and reminds readers that both electricity and heat must be accounted for in the analysis.

Summary

The articles highlighted in this blog post represent just a small fraction of the many resources available for building a common understanding and better collaboration among all researchers working on the improvement of green hydrogen technologies. When the COVID pandemic shut down laboratory work and travel for many people, the research community carried on with enthusiasm.

Online seminars and working groups held openly and without cost have brought scientists together across disciplines and from around the world. For example, the Electrochemical Online Colloquium was started in 2021. This ongoing series of lectures addresses essential topics in electrochemistry by providing educational content alongside the personal perspective of expert speakers.

The electrochemical community is acutely aware of the importance of transitioning to sustainable and climate-safe energy and chemical processes. Energy storage and conversion through green hydrogen is a promising strategy that requires scientific advancement to thrive. Thankfully, researchers from across many disciplines are bringing their skills and creativity to this topic while the electrochemical community continues to drive collaborative efforts and share their core knowledge.

To find out more about associated topics, download these free Application Notes from Metrohm Autolab.

References

[1] Green Hydrogen Cost Reduction: Scaling up Electrolysers to Meet the 1.5°C Climate Goal; International Renewable Energy Agency: Abu Dhabi, 2020.

[2] McCrory, C. C. L.; Jung, S.; Peters, J. C.; et al. Benchmarking Heterogeneous Electrocatalysts for the Oxygen Evolution Reaction. J. Am. Chem. Soc. 2013, 135 (45), 16977–16987. doi:10.1021/ja407115p

[3] Niu, S.; Li, S.; Du, Y.; et al. How to Reliably Report the Overpotential of an Electrocatalyst. ACS Energy Lett. 2020, 5 (4), 1083–1087. doi:10.1021/acsenergylett.0c00321

[4] Jerkiewicz, G. Standard and Reversible Hydrogen Electrodes: Theory, Design, Operation, and Applications. ACS Catal. 2020, 10 (15), 8409–8417. doi:10.1021/acscatal.0c02046

[5] Nutting, J. E.; Gerken, J. B.; Stamoulis, A. G.; et al. “How Should I Think about Voltage? What Is Overpotential?”: Establishing an Organic Chemistry Intuition for Electrochemistry. J. Org. Chem. 2021. doi:10.1021/acs.joc.1c01520

[6] Lamy, C.; Millet, P. A Critical Review on the Definitions Used to Calculate the Energy Efficiency Coefficients of Water Electrolysis Cells Working under near Ambient Temperature Conditions. J. Power Sources 2020, 447, 227350. doi:10.1016/j.jpowsour.2019.227350

Post written by members of the Metrohm Autolab group, Utrecht, The Netherlands.
Cyclic voltammetry (CV) – the essential analytical technique for catalyst research

Cyclic voltammetry (CV) – the essential analytical technique for catalyst research

Cyclic voltammetry (CV) is the backbone of most electrochemical research and is an essential electrochemical technique that allows researchers to explore candidate catalysts in greater depth. When coupled with modeling, a systematic goal-focused protocol will supply a range of data that will inform the user of more novel techniques and complex setups. This disciplined approach will save time in the long run, and is especially helpful to those who may have limited access to electrochemical instrumentation in a busy laboratory.
This article provides an overview of possible research goals when using CV along with relevant examples from scientific literature with the approach in action.
Electrocatalysis (ECAT) is defined as the catalysis of an electrode reaction. The electrocatalytic effect leads to an increase of the standard rate constant of the electrode reaction—resulting in a higher current density, or to a decrease in overpotential when other rate limiting steps are involved. The study of an electrocatalytic process requires characterization of the mechanism and kinetics of the electrode reaction. Forced convection methods can offer the advantage of reducing the contributions from mass-transport and providing direct access to the kinetic and mechanistic information.

In the last decade, a greater understanding of critical electrochemical transformations has been established, particularly those that involve water, hydrogen, and oxygen [1]. The expansion of our understanding in this realm was only possible because of the use of critical electrochemical techniques. This has allowed researchers to not only explore a wider variety of catalysts, but explore them in greater detail.

To respond to the potential volume of exploration which may discover more cost-effective and renewable materials that are not at the stage of critical depletion, a systematic approach to analytical research is required.

As always, new techniques are constantly being developed, but the gold standard technique of exploration of catalysts with cyclic voltammetry (CV) is still recommended as the starting point for researchers.
Instrumentation for CV analysis of catalysts from Metrohm Autolab.

Experimental Goals and Procedure Selection

To effectively explore a candidate catalyst, it is important to consider what the experimental goal is and then choose the procedure accordingly. Examples of possible goals are listed in the following sections along with suggested procedures and/or techniques.

Exploring a new system

Determine the (E) stability window of the electrolyte [2]

Method: Perform CV measurement in broad voltage (E) window, using an inert electrode (e.g. glassy carbon) and investigate the general redox behavior of the electrocatalyst material.

 

Investigate the general redox behavior of the electrocatalyst material [2]

Method: Perform CV measurement in a broad voltage (E) window, using a well understood electrolyte and new electrocatalyst.

Determine the electrode surface area for quantitative comparisons [3–5]

Method: Various methods that are material dependent: using a well-defined surface reaction (e.g. stripping or oxide formation) or analysis of electrochemical double layer capacitance (Cdl).

 

Investigate the stability of the electrocatalyst [6, 7]

Method: Perform repetitive CV measurements over several hundred cycles or during several days.

Probing a specific electrochemical reaction

Determine if a reaction is reversible (fast electron transfer kinetics), quasi reversible (slow kinetics), or irreversible (governed by other factors) [8, 9

Method: Perform CV measurements at various scan rate values, then examine dependencies for the peak position (Epeak) and peak height (Ipeak) on the scan rate.

Determine the apparent activation energy of the reaction [10]

Method: Perform CV measurements at various temperatures, then analyze electrochemical Arrhenius plots of log j vs. 1/T.

Combining CV with additional techniques to confirm results and deepen understanding

Determine the molecular structure of products or intermediates at a specific instance of the reaction [9–12]

Method: Perform CV measurement with in-situ spectroscopic determination (spectroelectrochemistry via UV/Vis/NIR or Raman spectroscopy).

Investigate material deposited or removed from the electrode surface during the electrochemical measurement [13]

Method: Measure the mass change at the electrode surface during a CV measurement using electrochemical quartz crystal microbalance (EQCM).

Investigate products and short-lived intermediates via their electrochemical response [14, 15]

Method: Perform bipotentiostat (two working electrodes) measurements in a ring/disk configuration (RRDE).

From action to reactions in the literature

This paper from the Nissan Fuel cell research center (NFCRC) summarizes the analytical approach for reduction of Pt loading in fuel cell catalyst layers (CL) [7]. Using a combined experimental and theoretical approach, they clearly outline the important properties required to measure experimentally or model to reach their goal of reducing the amount of Pt used in the CL. 

Focal parameters for exploration:

 

1. Catalyst Microstructure

Research goal: Determine the electrode surface

Using microscope images combined with the Cdl (double layer capacitance) and ionomer coverage, the researchers were able to analyze and quantify their catalyst layer. They used CV to determine ionomer coverage over the carbon by comparing Cdl values (wet versus dry).

 

2. Transport Properties

Research goal: Investigate material deposited or removed from the electrode surface during the electrochemical measurement

Additional research investigating the electrode surface was performed with CV. Using a rotating disk electrode, the researchers were able to determine the gas transport resistance by measuring the ORR (oxygen reduction reaction). CV also allowed the determination of the Pt roughness factor.

 

3. I-V performance

Research goal: Use CV I-V to calculate the fuel cell performance

I-V performance is a typical measurement for the overall performance of the fuel cell. A potentiostat is needed to measure the actual I-V curve in order to determine the Pt loading so that the I-V performance can be interpreted and compared among various samples.

    This paper illustrates the value of systematic exploration of catalysts with CV to give a comprehensive overview of attributes, structure, and reactions before moving on to more complex setups.

    Your initial investigations with CV may not provide all of the answers at first glance, but you can then move on to more complex setups and experiments with complete insight.

    Curious about electrochemistry?

    Metrohm has you covered.
    References

    [1] Seh Z. W.; Kibsgaard J.; Dickens C. F.; et al. Combining Theory and Experiment in Electrocatalysis: Insights into Materials Design. Science 2017, 355, 6321. doi:10.1126/science.aad4998

    [2] Kübler, P.; Sundermeyer, J. Ferrocenyl-Phosphonium Ionic Liquids – Synthesis, Characterisation and Electrochemistry. Dalton Trans. 2014, 43 (9), 3750–3766. doi:10.1039/C3DT53402B

    [3] Biegler, T.; Rand, D. A. J.; Woods, R. Limiting Oxygen Coverage on Platinized Platinum; Relevance to Determination of Real Platinum Area by Hydrogen Adsorption. J. Electroanal. Chem. Interfacial Electrochem. 1971, 29 (2), 269–277. doi:10.1016/S0022-0728(71)80089-X

    [4] Trasatti, S.; Petrii, O. A. Real Surface Area Measurements. Int. Union Pure Appl. Chem. 1991, 63 (5), 711–734. doi:10.1351/pac199163050711

    [5] Kinkead, B.; van Drunen, J.; Paul, M. T. Y.; et al. Platinum Ordered Porous Electrodes: Developing a Platform for Fundamental Electrochemical Characterization. Electrocatalysis 2013, 4 (3), 179–186. doi:10.1007/s12678-013-0145-2

    [6] Pilapil, B. K.; van Drunen, J.; Makonnen, Y.; et al. Ordered Porous Electrodes by Design: Toward Enhancing the Effective Utilization of Platinum in Electrocatalysis. Adv. Funct. Mater. 2017, 27 (36), 1703171. doi:10.1002/adfm.201703171

    [7] Xing, L.; Hossain, M. A.; Tian, M.; et al. Platinum Electro-Dissolution in Acidic Media upon Potential Cycling. Electrocatalysis 2014, 5 (1), 96–112. doi:10.1007/s12678-013-0167-9

    [8] Rountree, E. S.; McCarthy, B. D.; Eisenhart, T. T.; et al. Evaluation of Homogeneous Electrocatalysts by Cyclic Voltammetry. Inorg. Chem. 2014, 53 (19), 9983–10002. doi:10.1021/ic500658x

    [9] Sokolov, S.; Sepunaru, L.; Compton, R. Taking Cues from Nature: Hemoglobin Catalysed Oxygen Reduction. Appl. Mater. Today 2017, 7, 82–90. doi:10.1016/j.apmt.2017.01.005

    [10] Barbosa, A. F. B.; Oliveira, V. L.; van Drunen, J.; et al. Ethanol Electro-Oxidation Reaction Using a Polycrystalline Nickel Electrode in Alkaline Media: Temperature Influence and Reaction Mechanism. J. Electroanal. Chem. 2015, 746, 31–38. doi:10.1016/j.jelechem.2015.03.024

    [11] Hernández, C. L.; González García M. B.; Santos , D. H.; et al. Aqueous UV-VIS Spectroelectrochemical Study of the Voltammetric Reduction of Graphene Oxide on Screen Printed Carbon Electrodes. doi:10.1016/j.elecom.2016.01.017

    [12] Görlin, M.; de Araújo, J. F.; Schmies, H.; et al. Tracking Catalyst Redox States and Reaction Dynamics in Ni-Fe Oxyhydroxide Oxygen Evolution Reaction Electrocatalysts: The Role of Catalyst Support and Electrolyte PH. J Am Chem Soc 2017, 139 (5), 2070–2082. doi:10.1021/jacs.6b12250

    [13]  Lee, C-L.; Huang, K-L.; Tsai, Y-L.; et al. A Comparison of Alloyed and Dealloyed Silver/Palladium/Platinum Nanoframes as Electrocatalysts in Oxygen Reduction Reaction. Electrochem. Commun. 2013, 280–285. doi:10.1016/j.elecom.2013.07.020

    [14] Vos, J. G.; Koper, M. T. M. Measurement of Competition between Oxygen Evolution and Chlorine Evolution Using Rotating Ring-Disk Electrode Voltammetry. J. Electroanal. Chem. 2018, 819, 260–268. doi:10.1016/j.jelechem.2017.10.058

    [15] Kocha, S. S.; Shinozaki, K.; Zack, J. W.; et al. Best Practices and Testing Protocols for Benchmarking ORR Activities of Fuel Cell Electrocatalysts Using Rotating Disk Electrode. Electrocatalysis 2017, 8 (4), 366–374. doi:10.1007/s12678-017-0378-6

    Post written by members of the Metrohm Autolab group, Utrecht, The Netherlands.
    Staircase or linear scans: two options for reliable electrochemical experiments

    Staircase or linear scans: two options for reliable electrochemical experiments

    Electrochemical experiments are performed by delivering and controlling a potential or current signal to the electrochemical cell/device under test and measuring its response through a potentiostat/galvanostat (PGSTAT). Here, two different options for performing different electrochemical experiments are discussed: linear and staircase scans, as well as some applications where one may be preferred over another.

    From analog to digital

    Before modern digital electronics were widely available, PGSTATs worked with analog electronics, and therefore delivered analog signals. Analog boards were expensive and time-consuming to produce and test. Moreover, controlling the equipment from a computer is done via digital communication and requires digital electronics.

    An analog signal is continuous, and it has virtually infinite resolution. On the other hand, a digital signal is written in discrete bits (0 and 1), so it is not continuous.

    Linear scans

    To better explain an analog signal, consider a linear sweep voltammetry (LSV) in potentiostatic mode, performed with an analog scan. Here, the applied voltage E versus time plot consists of a straight line between the initial and end potentials. The potential interval between two consecutive data points and the scan rate define the interval time—the slope of the E versus time plot (Figure 1).

    Figure 1. A typical linear scan from an initial and an end potential. The interval time and the measurement time are also shown here.

    The current resulting from the application of the LSV is measured at the end of the interval time. The measurement time defines the duration of the sampling. The current is composed of a capacitive part ic (given by the charging of the double layer), and a faradaic part if.

    A double layer is formed when a potential is applied to an electrode. Then, current flows to the electrode, which becomes charged. Ions from the bulk solution migrate to the surface to balance this charge. Therefore, a layer of ions at the interface between the electrode and the electrolyte builds up, forming the equivalent of a capacitor.

    Learn more about the principles and characterization of capacitors in our free Application Note.

    The faradaic current is the result of the electrochemical reactions occurring at the working electrode | electrode and counter electrode | electrolyte interfaces, and it changes with the scan rate either linearly or with the square root of the scan rate, depending on the type of electron transfer.

    The capacitive current resulting from a linear scan iC,ls is a constant value given by the product of the double layer capacitance Cdl and the scan rate.

    Find out more about the differences between linear and staircase cyclic voltammetry on a commercial capacitor in our free Application Note.

    Staircase scans

    When modern digital electronics became more commercially available and economically feasible, PGSTAT manufacturers adopted them, together with personal computers, to control PGSTATs. This allowed researchers to create more complex procedures as well as to perform data analysis via software. Metrohm Autolab was the first company to deliver computer controlled PGSTATs to the market back in 1989.

    In the case of a digital scan, the applied potential versus time plot between an initial and end potential has the typical «staircase» shape of a digitized signal. The interval time tint defines the duration of each step, while the step potential Estep defines the potential difference between two consecutive steps (Figure 2).

    Figure 2. A typical staircase scan profile. The step potential Estep is shown along with the interval time and the measurement time.

    The resulting current is measured at the end of the step. The measurement time defines the sampling time.

    In a digital scan, the step potential  Estep results in a capacitive current iC,ss which rises almost immediately up to the maximum value allowed by the current range, lim(CR), and then it decays exponentially as time constant t = RC. After the decay of the capacitive current, the faradaic current if is predominant.

    The current is measured at the end of the step in order to remove the capacitive current and collect only the faradaic one (Figure 3).

    Figure 3. Potential step (in blue) and current profile for a staircase scan. The current profile is divided into capacitive current iC,ss (black line) and faradaic current if (purple line). Total current itot is shown in dark red. The measurement (sampling) time is also shown here. For clarity, the decay of the capacitive current and the decay of the faradaic current are not in scale.

    Application examples: staircase or linear scan?

    Capacitors

    Some electrochemical processes can result in a capacitive current, having a characteristic time comparable to the charging of the double layer. In such cases a digital scan would neglect such capacitive currents and all of the information contained within them.

    This is the case of highly capacitive cells, such as capacitors and supercapacitors.

    In Figure 4, cyclic voltammograms at different scan rates of a commercial 1 µF capacitor are shown. The diagram on the left shows the results from the digital scan, and on the right are the results from the analog scan [1].

    Figure 4. Cyclic voltammograms of a 1 µF capacitor at different scan rates. Left: the cyclic voltammogram resulting from a digital scan. Right: the cyclic voltammogram resulting from an analog scan.

    It is pretty clear that the digital scan results do not contain any information about the charge/discharge of the capacitor, while the analog scan results have the expected shape of a capacitor’s cyclic voltammograms.

    Adsorption/desorption processes

    Another application example includes cells in which fast adsorption/desorption of species at the electrode surface occurs in a short time, like the adsorption/desorption of hydrogen as part of the electrochemical behavior of platinum submerged in an aqueous solution of sulfuric acid (Figure 5).

    Figure 5. The cyclic voltammogram of a Pt working electrode immersed in a 0.5 mol/L H2SO4 aqueous solution. The reference is a Ag/AgCl 3M KCl electrode, while the counter electrode is a Pt electrode.

    Here, the fast adsorption/desorption of hydrogen occurs at time scales that are similar to the charging of the double layer in the capacitor example. Therefore, the linear scan is the preferred option, compared to the digital staircase scan which is unable to capture the hydrogen adsorption/desorption (Figure 6) [2].

    Figure 6Top: linear cyclic voltammograms of a Pt working electrode immersed in a 0.5 mol/L H2SO4 aqueous solution at different scan rates. Bottom: staircase cyclic voltammograms of the same setup at the same scan rates.

    Redox reactions

    Another example of experiments in which the capacitive current should not be neglected are redox reactions in which the electron transfer is very fast. In these situations, the charge transfer resistance is very small and the cyclic voltammogram results in redox peaks which are symmetrical over the potential axes. Examples include redox reactions on species adsorbed on the working electrode surface [3].

    VIONIC: the future of electrochemistry

    The most recent generation of PGSTATs, such as VIONIC, are equipped with electronics that allow to users perform analog scans without the drawbacks mentioned earlier. This gives researchers the opportunity to choose the type of scan according to the type of systems being studied, the materials, and the importance of the capacitive current for the outcomes of the research.  

    Learn more about VIONIC

    Maximum experimental possibilities, intelligent software, and the most complete data.

    References

    [1] Locati, C. Comparison between linear and staircase cyclic voltammetry on a commercial capacitor, Metrohm AG: Herisau, Switzerland, 2021. AN-EC-026

    [2] Locati, C. Study of the hydrogen region at platinum electrodes with linear scan cyclic voltammetry – How VIONIC powered by INTELLO can be used to characterize processes at the Pt-electrolyte interface, Metrohm AG: Herisau, Switzerland, 2021. AN-EC-025

    [3] Chi, Q.; Zhang, J.; Andersen, J. E. T.; Ulstrup, J. Ordered Assembly and Controlled Electron Transfer of the Blue Copper Protein Azurin at Gold (111) Single-Crystal Substrates. J. Phys. Chem. B 2001, 105 (20), 4669–4679. https://doi.org/10.1021/jp0105589

    Post written by Dr. Corrado Locati, Application Specialist at Metrohm Autolab, Utrecht, The Netherlands.

    Spectroelectrochemistry: shedding light on the unknown

    Spectroelectrochemistry: shedding light on the unknown

    The combination of two well-known analytical techniques, electrochemistry and spectroscopy, gives rise to spectroelectrochemistry (SEC), an established scientific methodology. This hybrid technology combines the advantages of each technique, offering the best of both worlds [1]. The word «spectroelectrochemistry» is the result of combining these two terms as two pieces of a puzzle that fit perfectly together.

    In this article, written for both beginners in the field as well as more experienced readers, we focus on introducing this technique from its beginnings to its advantages in research, and then discuss new systems and solutions that will make it easier to work on the multitude of applications that spectroelectrochemistry can offer. 

    Shedding light, in the literal sense of the phrase, on electrochemical knowledge and procedures. Spectroelectrochemistry offers analysts more information by being able to record both an optical and an electrochemical signal at the same time to obtain new data.

    This is a multi-response method—it studies the process of electrochemical reactions with simultaneous optical monitoring. Spectroelectrochemistry provides two individual signals from a single experiment, which is a very powerful feature to obtain critical information about the studied system. Moreover, the autovalidated character of spectroelectrochemistry confirms the results obtained by two different routes. Find out more about this topic by downloading our free Application Note below.

    Spectroelectrochemistry allows researchers to collect molecular, kinetic, and thermodynamic information from the reactants, intermediates, and/or products involved in electron transfer processes. Thus, it is possible to perform spectroelectrochemical studies on a broad range of molecules and different processes including: biological complexes, polymerization reactions, nanomaterial characterization, analyte detection, corrosion mechanisms, electrocatalysis, environmental processes, characterization of memory devices, and much more!

    Ultimately, different kinds of information is obtained depending on the spectral range used. UV-VIS spectroscopy provides molecular information related to the electronic levels of the molecules, the NIR region provides data associated with the vibrational levels, and the Raman spectrum provides very specific information about the structure and composition of the sample due to the fingerprinting characteristics of this technique.

    Electromagnetic Spectrum
    Diagram of the electromagnetic spectrum.

    The beginnings of spectroelectrochemistry

    Theodore Kuwana, Ph.D. in chemistry and specialist in spectroelectrochemistry, bioelectroanalytical chemistry and modified electrodes.

    This analytical technique was developed in the 1960’s, and became popularized by Professor Theodore Kuwana and other researchers [2]. They had begun to work with transparent electrodes to study a simultaneous process—measuring the charge and absorbance (at the same time) when a beam of light passes through the electrode. As a result, they developed transparent electrodes and this marked the beginning of concurrent electrochemical and UV-VIS absorption measurements.

    These so-called «optically transparent electrodes» (OTEs) were developed to carry out the combination of optical and electrochemical experiments. Some of the most commonly used OTEs began as oxide doped with antimony on glass, then developed into different thin films of gold or platinum on quartz, followed by germanium electrodes for IR wavelengths, as well as pure gold and platinum micromeshes (where the holes provide the required transparency to light). However, not all spectroelectrochemical configurations require transparent electrodes. For more information, download the electrode reference flyers from Metrohm DropSens to properly work with the different spectroelectrochemical techniques.

    A selection of Metrohm DropSens references. Left: C013 for in-situ surface Raman spectroscopy. Right: P10 optically transparent and specially designed for spectroelectrochemical applications.

    Download the free flyers for these electrodes below for further information.

    The first published paper on spectroelectrochemistry [2], in which Dr. Kuwana participated, describes the use of tin oxide-coated glass surfaces (optically transparent electrodes) for following the absorbance changes of different electroactive species during electrolysis. Since then, the number of works and investigations based on this technique have grown steadily.

    Spectroelectrochemistry publications have increased significantly since its discovery in the 1960’s (results of searching «Spectroelectrochem*» as a term in Scopus as of June 2021).

    Take a look for yourself to see how things have changed in the last several decades!

    An array of spectroelectrochemical techniques to choose from

    The following graphic is classified according to the combination of different electrochemical and spectroscopic methods. The general classification is based on the spectroscopic technique: ultraviolet (UV), visible (Vis), photoluminescence (PL), infrared (IR), Raman, X-ray, nuclear magnetic resonance (NMR), and electron paramagnetic resonance (EPR).

    Spectroelectrochemistry (SEC) is the combination of spectroscopy and electrochemistry.

    In recent years, significant advances have occurred regarding the design, development, and possibilities offered by instruments for working with spectroelectrochemical techniques. Also, the assemblies and the connections between products and accessories that facilitate the use of this equipment have improved in recent decades, contributing to make research and experiments in this field easier and more affordable.

    The evolution of spectroelectrochemical instrumentation

    Traditionally, the configuration for spectroelectrochemical analysis consists of two instruments: one spectroscopic instrument and the other for electrochemical analysis. Both instruments are connected independently to the same spectroelectrochemical cell and are generally not usually synchronized. In addition, each instrument is controlled by a different (and specific) software in each case, so two programs are also needed to interpret each signal and yet another external software for the processing and analysis of the data obtained by the first two programs. Finally, it must be considered that synchronization is not guaranteed, making the performance of experiments and tests with this configuration slow, complex, and costly.

    This detached spectroelectrochemical setup displays the complexity of various software and programs used, showing that different systems are not able to obtain actual synchronized electrochemical measurements and data (click to enlarge).

    Metrohm DropSens took this opportunity to create something that did not exist before—a revolution in the state-of-the-art of spectroelectrochemistry: the SPELEC line of instruments which are fully integrated, synchronized solutions that offer much more versatility to researchers. The devices include all of the components needed to work with spectroelectrochemical techniques in a simple way and in a single system with a (bi)potentiostat/galvanostat, the light source, and the spectrometer (depending on the selected spectral range).

    Find out more about SPELEC, the next-generation tool for spectroelectrochemical research on our website.

    The SPELEC systems from Metrohm DropSens consist of one device and one software—a fully integrated, easy to use, practical setup for researchers.

    These designs and configurations simplify the work, processes, and spectroelectrochemical measurements as well because only a single system and a single software are needed. In the case of the SPELEC solution, its advanced dedicated software (DropView SPELEC) is a specific program that controls the instrument, obtains the electrochemical and spectroscopic signals simultaneously, and also allows users to process and analyze the data together in a single step. It’s really that simple!

    The future of spectroelectrochemistry: SPELEC systems and software

    One instrument and one software: Metrohm DropSens SPELEC has everything you need for your spectroelectrochemical experiments while saving laboratory space and valuable time. SPELEC instruments offer the combinations of electrochemistry and UV-Vis, Vis-NIR, or even Raman spectroscopy in a single measurement with several different instrument options available (see below). Everything is integrated which allows more tests in less time, multiple spectra, a full range of accessories, and research flexibility with the different configurations available.

    Several options are available depending on the spectral range needed:

    SPELEC: 200–900 nm (UV-VIS)
    SPELEC NIR: 900–2200 nm
    SPELEC RAMAN: 785 nm laser
    (other wavelengths available upon request)
    SPELEC 1050: 350–1050 nm (VIS-NIR)

    DropView SPELEC is a dedicated and intuitive software that facilitates measurement, data handling, and processing. With this program, you can display electrochemical curves and spectra in real time and follow your experiments in counts, counts minus dark, absorbance, transmittance, reflectance, or Raman shift. As far as data processing is concerned, DropView SPELEC offers a wide variety of functions including graph overlay, peak integration and measurement, 3D plotting, spectral movie, and more.

    Testimonial from the University of Burgos on the integrated SPELEC system from Metrohm DropSens.

    SPELEC instruments are very versatile, and although they are dedicated spectroelectrochemical instruments, they can also be used for electrochemical and spectroscopic experiments. They can be used with any type of electrodes (e.g., screen-printed electrodes, conventional electrodes, etc.) and with different spectroelectrochemical cells. Optical and electrochemical information is obtained in real time/operando/dynamic configuration. The main advantages of spectroelectrochemical techniques can be summarized as follows:

    • they simultaneously provide information obtained by two different techniques (electrochemistry and spectroscopy) in a single experiment
    • qualitative studies and quantitative analyses can be performed
    • high selectivity and sensitivity
    • spectroelectrochemistry is used in a wide variety of different fields due to its great versatility
    • new configurations facilitate the performance of spectroelectrochemical experiments, saving time, samples, costs, etc.

    Learn more about the next-generation tool for spectroelectrochemical research on our website!

    SEC analysis techniques: suitable for multiple applications

    The characteristics of spectroelectrochemistry allow the constant development of new and broad applications in several different fields. Read on below to discover the capabilities of this technique.

    Materials science: characterization of specific properties of carbon materials, quantum dots, composites, nanoparticles, Janus materials, polymers, as well as stability studies, determination of photochemical properties, development of new materials, etc.

    For more information, download our free related Application Note below.

    Sensing: selective and sensitive detection, rapid quantification of a huge variety of analytes, diagnostic tool, development of new methodologies and sensors, etc. [3].

    Organic and inorganic chemistry: study of the properties and structure of different compounds, analysis of kinetic reactions, determination of electron transfer capacity, etc. [4].

    Corrosion: evaluation of protective films as corrosion inhibitors, determination of electrode stability and reversibility, monitoring of layer and sublattice generation, improvement of protective properties of coating materials, etc.

    Energy storage: monitoring of exchange and discharge cycles, determination of oxidation/reduction levels, characterization of new electrolytes for batteries, understanding of doping and splitting processes in solar cells, etc.

    Electrocatalysis: characterization and comparison of the electrocatalytic activity of different catalysts, identification of intermediate species and their structural changes, elucidation of the reaction mechanism, etc. [5].

    Life sciences: study of biological processes, characterization of molecules used in biotechnology, biochemistry or medicine, determination of antioxidant activity, etc.

    Environment: identification and quantification of pesticides, dyes, and pollutants, monitoring of degradation and filtration processes, etc. [6]

    Download our free related Application Note for more information.

    Others: characterization of new materials for memory devices, comparison of minerals, identification of pigments, oils, and pastes, etc.

    Learn even more about spectroelectrochemistry (SEC) and what it can do for your research by downloading our free brochure.

    Contact us

    to discuss how spectroelectrochemistry can boost your research.

    References

    [1] Kaim, W.; Fiedler, J. Spectroelectrochemistry: The Best of Two Worlds. Chem. Soc. Rev. 2009, 38 (12), 3373. doi:10.1039/b504286k

    [2] Kuwana, T.; Darlington, R. K.; Leedy, D. W. Electrochemical Studies Using Conducting Glass Indicator Electrodes. Anal. Chem. 1964, 36 (10), 2023–2025. doi:10.1021/ac60216a003

    [3] Martín-Yerga, D.; Pérez-Junquera, A.; González-García, M. B.; Perales-Rondon, J. V.; Heras, A.; Colina, A.; Hernández-Santos, D.; Fanjul-Bolado, P. Quantitative Raman Spectroelectrochemistry Using Silver Screen-Printed Electrodes. Electrochimica Acta 2018, 264, 183–190. doi:10.1016/j.electacta.2018.01.060

    [4] Perez-Estebanez, M.; Cheuquepan, W.; Cuevas-Vicario, J. V.; Hernandez, S.; Heras, A.; Colina, A. Double Fingerprint Characterization of Uracil and 5-Fluorouracil. Electrochimica Acta 2021, 388, 138615. doi:10.1016/j.electacta.2021.138615

    [5] Rivera-Gavidia, L. M.; Luis-Sunga, M.; Bousa, M.; Vales, V.; Kalbac, M.; Arévalo, M. C.; Pastor, E.; García, G. S- and N-Doped Graphene-Based Catalysts for the Oxygen Evolution Reaction. Electrochimica Acta 2020, 340, 135975. doi:10.1016/j.electacta.2020.135975

    [6] Ibáñez, D.; González-García, M. B.; Hernández-Santos, D.; Fanjul-Bolado, P. Detection of Dithiocarbamate, Chloronicotinyl and Organophosphate Pesticides by Electrochemical Activation of SERS Features of Screen-Printed Electrodes. Spectrochim. Acta. A. Mol. Biomol. Spectrosc. 2021, 248, 119174. doi:10.1016/j.saa.2020.119174

    Post written by Dr. David Ibáñez Martínez (Product Specialist Spectroelectrochemistry) and Belén Castedo González (Marketing and Communication) at Metrohm DropSens, Oviedo, Spain.

    Does counter electrode (CE) size matter?

    Does counter electrode (CE) size matter?

    To begin, let’s go back to the year 1950 when metallurgists and chemists tried to shine a light on a fascinating electrochemical phenomenon originally discovered in the 17th century by the chemist Sir Humphry Davy [1].

    Sir Humphry Davy (1778–1829) was credited with many discoveries in the field of electrochemistry.

    If you dip a wire made of iron (or as electrochemists say: an iron electrode) into diluted sulfuric acid (which is considered the electrolyte), it instantly starts to dissolve—it corrodes. If you then insert another electrode which does not corrode (e.g. platinum), and connect the iron electrode to the negative pole of a current source, and the platinum wire (electrode) to the positive pole, the iron dissolution will slow down or even stop, depending on the voltage applied.

    On the other hand, if you connect the iron electrode to the positive pole and raise the voltage from very low values to higher ones, the dissolution grows exponentially with the increasing voltage.

    However, above a certain current limit (and depending on the electrode area, electrolyte composition, and temperature), the current suddenly drops to very low values, and the iron electrode stops dissolving. This phenomenon was detected by Michael Faraday, and he called it «passivation». This phenomenon has been subject of controversy and disputes until the 1950s when a better understanding was possible with the invention of the modern potentiostat (Figure 1).

    Figure 1. Basic line diagram of a potentiostat/galvanostat.

    In experiments where the ohmic drop may be high (e.g., in large-scale electrolytic or galvanic cells or in experiments involving nonaqueous solutions with low conductivities), a three-electrode electrochemical cell is preferable. In this arrangement, the current is passed between the working electrode (WE) and a counter (or auxiliary) electrode (CE).

    Learn more about the ohmic drop in our free Application Notes.

    The counter electrode can be made of any available electrode material because its electrochemical properties do not affect the behavior of the working electrode of interest. It is best to choose an inert electrode so that it does not produce any substances by electrolysis that will reach the working electrode surface and cause interfering reactions there (e.g., platinum or carbon). Because the current flows between the WE and the CE, the total surface area of the CE (source/sink of electrons) must be larger than the area of the WE so that it will not be a limiting factor in the kinetics of the electrochemical processes under investigation.

    Sometimes it is placed in a compartment separated from the working electrode by a sintered-glass disk or other separator (Figure 2). Bulk electrolysis experiments typically require much longer times than electroanalytical experiments, so separation of the counter electrode is required.

    Figure 2. Gastight electrochemical cell for CO2 reduction study (click to enlarge).

    The potential of the working electrode is monitored relative to a separate reference electrode (RE), positioned with its tip nearby (with a Luggin capillary as shown in Figure 3). The potentiostat used to control the potential difference between the working electrode and the reference electrode has a very high input impedance so that a negligible current flows through the reference electrode. Consequently, the potential of the reference electrode will remain constant and equal to its open-circuit value. This three-electrode arrangement is used in most electrochemical experiments.

    The counter electrode is used to close the current circuit in the electrochemical cell. It is usually made of an inert material (e.g., Pt, Au, graphite, or glassy carbon) and it hosts a redox reaction which occurs at the CE surface that balances the redox reaction at the surface of the WE. The products of this reaction can diffuse to the WE and interfere with the redox reaction occurring at that site. However, in electroanalytical experiments such as cyclic voltammetry (CV), the time scale of the experiment is too short for this diffusion to be able to cause significant interferences. Therefore, in most cases there is no need to place the CE in a separate compartment, as shown in the electrochemical cell in Figure 3.

    Figure 3. Metrohm Autolab 1 liter corrosion cell labelled with electrodes.

    The potential profile in an actual cell depends on the electrode shapes, geometry, solution conductance, and more. If the reference electrode is placed anywhere except precisely at the electrode surface, some fraction of an uncompensated potential, iRu (due to the uncompensated resistance, Ru) will be included in the measured potential. Even when the tip of the reference electrode is designed for very close placement to the working electrode by use of a fine tip (Luggin capillary, also known as a Luggin-Haber capillary), some uncompensated resistance usually remains. Modern electrochemical instrumentation includes circuitry for electronic compensation of the iRu term [2].

    As mentioned earlier, the electrochemical reaction of interest takes place on the working electrode, and the electron transfer there will generate the measured current which flows between the WE and CE. As a general rule for accurate current measurements and an unhindered flow of electrons in the cell, the counter electrode should be three times larger than the working electrode. The kinetics of solvent electrolysis are generally slow, so the only way to ensure the CE reaction can sustain the required cell current is to significantly increase the surface area (e.g., with Pt gauze or a Pt rod/sheet).

    However, in poorly conductive media (or high currents), when positioning the counter electrode in the cell (i.e., for the cell geometry), it is worth considering where the field lines between the WE and CE will go, and whether the WE will experience a uniform field. It is generally recommended to move the counter electrode away from the working electrode, or even to put it behind a separator, unless you are certain that the WE reaction is insensitive to pH. The CE reaction sustains the current flow, but it is often unknown exactly what kind of reactions are occurring at the counter electrode. For most aqueous electrochemistry experiments this is likely to be solvent electrolysis, which leads to a change in the pH.

    When the application requires, the potential of the counter electrode can be monitored during the experiment with the S2 electrode of VIONIC. Find out more in our free Application Note.

    Alternative counter electrode materials

    Platinum is expensive, and it is too costly to use for large CE areas. Suitable alternative electrode materials include nickel-based alloys or carbon. Be aware that nickel-based alloys may passivate, and carbon will be oxidized at high potentials of the CE. Therefore, those materials should have a sufficient area to avoid strong polarization.

    Platinized titanium is a good choice when larger counter electrode areas are required. Platinized titanium is produced either in the form of sheets or mesh grids. Mesh grids (Figure 4) have very desirable properties: a large active area compared to the geometric area, and the electrolyte is able to flow through the counter electrode.

    Figure 4. Example of wire mesh grid suitable for use as a counter electrode.

     Also, at the counter electrode, a voltage drop occurs across the metal-electrolyte interface. To reduce this drop, it may be useful to use platinum covered with platinum black to increase the roughness, and consequently, the active surface area.

    Final notes

    Size matters in typical electrochemical measurements. Larger counter electrodes create an unconstrained current flow between WE and the CE, leading to more stable and insightful experiments. It is equally important that the overall cell configuration provides the required current density distribution. Thus, a counter electrode of the same size as the working electrode, mounted parallel to it, may optimize the current distribution without significant adverse effects from the size of the counter electrode.

    The reaction occurring at the CE should be fast so that the potential drop between the counter electrode and the electrolyte does not limit the polarization that can be applied.

    The products of the reaction occurring at the CE should not contaminate the solution. In practice, there will always be an electrochemical reaction at the counter electrode, and the products of that reaction should be harmless or able to be easily removed. Inert electrodes such as platinum or graphite are often used, in which case the reaction products are usually gases (oxygen or chlorine when anodic, or hydrogen when cathodic) that can be removed by bubbling air or nitrogen past the counter electrode (although there may also be a pH change at the CE).

    Curious about electrochemistry?

    Metrohm has you covered.

    References and suggested further reading

    [1] Knight, D. Humphry Davy: Science and Power (Volume 2 of Cambridge Science Biographies); Cambridge University Press: Cambridge, UK, 1998.

    [2] Bard, A. J.; Faulkner, L. R. Electrochemical Methods: Fundamentals and Applications, New York: Wiley, 2001, 2nd ed. Russian Journal of Electrochemistry, 2002, 38, 1364–1365. doi:10.1023/A:1021637209564

    [3] Yang, W., Dastafkan, K., Jia, C., et al. Design of Electrocatalysts and Electrochemical Cells for Carbon Dioxide Reduction Reactions. Adv. Mater. Technol. 2018, 3, 1700377. doi:10.1002/admt.201700377

    [4] Cottis, R. A. 2.30 – Electrochemical Methods. In Shreir’s Corrosion; Cottis, B., Graham, M., Lindsay, R., Lyon, S., Richardson, T., Scantlebury, D., Stott, H., Eds.; University of Manchester: Manchester, UK, 2010; Vol. 2, pp 1341–1373. doi:10.1016/B978-044452787-5.00068-8

    [5] Vanýsek, P. Impact of electrode geometry, depth of immersion, and size on impedance measurements. Canadian Journal of Chemistry 1997, 75(11), 1635–1642. doi:10.1139/v97-194

    Post written by Martijn van Dijk, Area Manager Electrochemistry at Metrohm Autolab, Utrecht, The Netherlands.