During seawater electrolysis, both oxygen and chlorine evolve at anode and their selectivity can be modulated through variation of surface and electronic structure of the electrocatalyst. In this context, the selectivity toward chlorine evolution reaction (CER) during seawater electrolysis using electrodeposited Cu-doped RuO 2 with lower doping concentration (2%) has been found to better than RuO 2 . Though Cu does not behave as an active site it reduces the binding energy of oxygen evolution reaction (OER) related intermediates (e.g. HO-, O-, HOO-) in neighboring Ru active sites and promotes both specific activity and selectivity of CER as suggested by both experimental and Density Functional Theory studies. However, due to aliovalent nature of Cu-dopant in RuO 2 host, phase segregation and surface enrichment of dopants occur with increase in dopant concentration which reduces the overall activity and selectivity toward CER. Furthermore, increase in Cu-dopant would lower surface oxygen vacancy formation energy and promotes additional lattice-oxygen-vacancy aided water dissociation pathway resulting in enhancement of selectivity of OER. The present work offers insight on catalyst design taking account of selectivity of chlorine and oxygen evolution during seawater electrolysis.

The compressive clamping pressure at the interface of gas‐diffusion‐layer (GDL) and current collector decreases the contact resistance between them though it reduces the porosity and surface roughness of electrocatalysts, which would in turn decrease the efficiency of an electrolyzer. We explore these issues of trade‐off between porosity versus contact resistance and provide a design heuristic for optimum clamping pressure. The present work provides an estimate of the optimal value of clamping pressure for an alkaline water electrolyzer having membrane electrode assembly (MEA), taking account of the variation in porosity of catalyst layers and contact resistance obtained via half‐cell studies performed at different pressures. Towards this, we define the performance‐index (Φ) which is the ratio of Faradaic current density and resistances resulting from contact‐interfaces in electrolyzers and we suggest that the maxima in Φ corresponds to optimum clamping pressure.