In catalyst design the surface of a material is altered as a means of modifying catalytic behaviour. By changing a surface's composition, nanostructure or even substrate, the binding energies of molecules to the surface and the reaction rate of different pathways can be tuned to promote certain reactions, and hopefully, suppress unwanted ones. In electrochemical CO2 reduction, the local environment can provide a similar function. Numerous experimental studies have particularly noted the tendency for higher local pH conditions to favour CO and multi-carbon products while suppressing H2 and CH4 on metals such as Ag and Cu. As shown in Fig. , when operating at higher current densities this effect is pushed to the extreme, even in highly buffered solutions. An important place to start is then to discuss the effect of pH on the selectivity of both CO2 reduction products and hydrogen evolution.