Bringing Clarity to Electrocatalysis: The Vital Role of Faradaic Efficiency Measurements

As we continually shift towards a cleaner, more sustainable future, our reliance on renewable electric power is increasing. With this dependency comes an unprecedented focus on harnessing this power to generate commodities such as chemicals and fuels, which is where electrocatalysis research comes into play. However, with the surge in activity in this field, ensuring accurate, reliable, and efficient processes is paramount. That's where the critical measurement of Faradaic efficiency (FE) takes center stage.

Understanding Faradaic Efficiency in Electrocatalysis

When we look at electrochemical reactions, total reaction rates can be continuously monitored through the electrical current flowing between two electrodes. But herein lies the challenge: the current doesn't necessarily give us specific information about the chemical reactions happening at the electrode interface. This is where Faradaic efficiency, a measure of the overall selectivity of an electrochemical process, comes in.

FE is determined by comparing the amount of product generated to what could theoretically be produced from the total charge passed, often expressed as a percentage. However, this information isn't always straightforward to decipher due to factors such as competing reactions, corrosion processes, and product crossover, which can complicate our understanding of the current's role in various Faradaic processes. That’s why having robust FE measurements are crucial, not only for understanding reaction selectivity but also for substantiating claims about activity and stability.

Faradaic Efficiency in Practice: The Electrocatalyst's Role

So how do we reliably measure Faradaic efficiency in an electrocatalyst? We do this by focusing on a specific subset of reactions that require protons and are relevant to electrified chemical manufacturing, including the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), carbon-dioxide reduction reaction (CO2RR), and the nitrogen reduction reaction (N2RR).

These reactions have practical applications in real-world scenarios. For instance, FE measurements are particularly important in reactions like CO2RR and N2RR, where competing HER cannot be ruled out solely based on thermodynamic arguments. Fortunately, with advancements in technology, modern mass spectrometry (MS) methods allow us to measure FEs nearly in real-time.

Ensuring Accuracy in FE Measurements

In the world of publication, the standard for reporting Faradaic efficiency is rigorous, with expectations varying depending on thermodynamic arguments. For example, the presence of multiple products at the applied potential at the working electrode, reactants or contaminants in the cell environment, and stability of all components of the electrocatalyst and its support, are factors that necessitate FE measurements. If there's an expectation of multiple products, including possible corrosion products, additional chemical product characterization is essential in assessing catalyst activity.

Methods for measuring Faradaic efficiency include titrations for liquid products of bulk electrolysis, colorimetric methods for NH3 production, measuring the volume of gas collected from the working electrode, electrochemical sensors, and fluorescence detectors. Furthermore, modern tools like gas chromatography (GC) and liquid chromatography (LC), particularly when combined with MS, allow researchers to validate the origin of products with precision.

The Future of Electrocatalysis and Faradaic Efficiency

It is crucial to stress the need for transparency in electrocatalysis research. Robust FE measurements, now approaching real-time quantification of products due to advancements in technology, are a vital part of that transparency. They allow for robust reporting of catalyst activity, selectivity, and stability.

In summary, researchers must shoulder the burden of proof to link ambiguous electrochemical data to the presumed chemical reaction of interest. Cost-effective methods involving titrations and gas collection are now so accessible that some FE measurement should be connected to any electrochemical current that could be assigned to more than one half-reaction.

As we march ahead in our pursuit of a sustainable future, the role of electrocatalysis will only grow, and so will the importance of measuring and understanding Faradaic efficiency. The electricity of tomorrow is being shaped today, and this electricity will be cleaner, more efficient, and more responsible, thanks in no small part to the diligent measurement and understanding of Faradaic efficiency.

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