Electrochemical and spectroscopic methods for evaluating molecular electrocatalysts

Modern energy challenges have amplified interest in transition metal-based molecular electrocatalysts for fuel-forming reactions. The activity of these homogeneous electrocatalysts, and the mechanisms by which they operate, can be uncovered using state-of-the-art electrochemical methods. Catalyst performance can be benchmarked according to metrics obtainable from cyclic voltammograms by analysis of catalytic plateau currents and peak potentials, as well as by foot-of-the-wave analysis. The application of complementary spectroscopic techniques, including spectroelectrochemistry, stopped-flow rapid mixing and transient absorption, are also discussed. In this Review, we present case studies highlighting the utility of these analytical methods in the context of renewable energy. Alongside these examples is a discussion of the theoretical underpinnings of each method, outlining the conditions necessary for the analysis to be rigorous and the type of information that can then be extracted. Homogenous transition metal electrocatalysts are topical owing to their role in processing electrical energy and mediating the synthesis of chemical fuels. Mechanisms can be uncovered using electrochemical techniques and data analyses, along with complementary spectroscopic techniques. This Review presents case studies highlighting the utility of these methods in the context of electrocatalysis for chemical fuel production.