Chapter 2
Electrocatalysis and the
splitting of water
Electrocatalysis can be described as the study of catalysing reactions taking
place at the interface between an electrode and an electrolyte. Already from
this general and simple description it is evident that the eld is highly interdisciplinary
and so one must be familiar with both surface science and physical
chemistry. The ultimate goal of electrocatalysis is to optimize the rate of electrochemical
reactions by a careful choice of electrode material 45. In water
electrolysis, the electrochemical generation of hydrogen and oxygen occurs at
such electrodes and their catalytic properties directly aect the eciency of the
process. This chapter serves as an introduction to the catalysis of water electrolysis.
Special attention will be given to the oxygen evolution reaction and
the development of nding catalysts for that reaction until now.
2.1 What is a catalyst?
Before describing the eld of electrocatalysis, it is useful to have a denition of
a catalyst. A catalyst increases the rate of a chemical reaction by providing a
surface where the reactants can bind and react to form products with a lower
energy barrier or activation energy 46. This phenomenon is illustrated in gure
2.1, where "red-black" and "red-red" reacts to form "red-red-black". In gas or
liquid phase the reaction proceeds slowly due to a high energy barrier despite
the fact that the product has a lower free energy. This is shown in the diagram
to the right in gure 2.1 as the blue curve. The slow rate is due to a short-lived