The conversion of renewable energy into storable, high value fuels is a key outstanding challenge in the transition to a carbon neutral economy. The primary source of electrons for the production chemically reduced fuel compounds is from the electrocatalytic oxidation of water. However, large quantities of energy are currently lost in the form of catalytic overpotential during water oxidation. This creates a challenge in scaling up electrolysis technology. To surmount these challenges, water oxidation activity must be improved using earth abundant catalysts. However, progress towards this goal is stymied by the complex ways in which applied voltage can drive water oxidation. This complexity is a result of the cooperative effects arising from interactions between oxidized species when large fraction of an electrocatalytic surface becomes oxidised. Competing, but not mutually exclusive, hypotheses, point to changes in activation energy¹ and changes in the catalytic mechanism involving the coupling of multiple oxidising equivalents during catalysis² as driving changes in rate constant and Tafel slope as a function of potential.

Cobalt compounds are used as water oxidation electrocatalysts for water oxidation across a wide rage of pH. However, the convolution of overlapping,  non-Nernstian redox processes and changes in catalytic mechanism complicate interpretation of Tafel slopes. In-situ spectroelectrochemistry can be used to separate redox driven changes in surface electronic structure from catalytic effects³. In this talk I demonstrate the construction and capabilities of a new potential and time operando spectroelectrochemical system to help resolve these questions in two model cobalt catalysts. First,  cobalt-iron hexacyanoferrate⁴, in which catalytic Co sites should be physically isolated from one another,^5,6 and secondly, amorphous cobalt phosphate oxide, in which Co centres interact during catalysts by oxo coupling and also via non-nernstian effects.^7,8 Using global analysis of a rich, 3d spectreoelectrochemial data set,  the potential dependence of the density of catalytically active states in both materials can quantified and compared. Time resolved spectral measurements as the catalysts relax from an operating potential to rest under open circuit conditions are used to access the kinetics of water oxidation.  These results show that contrast to cobalt phosphate oxide, catalysis in cobalt hexacyanoferrate shows negligible cooperative effects, both in terms of an enthalpic change in surface reactivity and multi-metallic catalysis, indicating a simple connection between the density of catalytic states and the Tafel slope.