Dual-doping Fe-Ni oxide for ultrahigh performance seawater oxidation by high-concentration electrolytes

Inhibiting the chlorine evolution reaction (CER) is of great significance for the design and development of oxygen evolution catalysts with high current density for seawater electrolysis. The KOH concentration plays a very important role in controlling the potential of chlorine evolution in seawater electrolysis. However, the effect of its concentration, especially the high one (for example, >1 M), on the OER activity of different catalysts has not been studied so far. Here, we found that the KOH concentration has different linear effects on the OER activity for different catalysts, and we first propose a novel concept named concentration activity coefficient (CAC) to express the linear relationship between the OER activity of the catalyst and the KOH concentration in seawater electrolysis. Based on CAC, we report a Co S-NiFe2O4 catalyst with ultrahigh oxygen evolution activity in the 3 M KOH + seawater. This is due to the strong electronic interaction between Co and S-NiFe2O4. At current densities of 500 mA cm−2 and 1000 mA cm−2, the overpotentials of Co S-NiFe2O4 are 270 mV, and 287 mV, respectively, which are much lower than those of the existing electrocatalysts. More promising, the new catalysts also showed a splendid Tafel slope of 18.8 mV dec−1 and a long catalytic lifetime in concentrated alkaline electrolyte. Our findings provide a better understanding of the correlation between the KOH concentration and the OER activity and open new avenues for design and development of electrocatalysts for the next generation of high OER activity in seawater electrolysis.