Direct electrolysis of pH-neutral seawater to generate hydrogen is an attractive approach for storing renewable energy. However, due to the anodic competition between the chlorine evolution and the oxygen evolution reaction (OER), direct seawater splitting suffers from a low current density and limited operating stability. Exploration of catalysts enabling an OER overpotential below the hypochlorite formation overpotential (≈490 mV) is critical to suppress the chloride evolution and facilitate seawater splitting. Here, a proton-adsorption-promoting strategy to increase the OER rate is reported, resulting in a promoted and more stable neutral seawater splitting. The best catalysts herein are strong-proton-adsorption (SPA) materials such as palladium-doped cobalt oxide (Co3- x Pdx O4 ) catalysts. These achieve an OER overpotential of 370 mV at 10 mA cm-2 in pH-neutral simulated seawater, outperforming Co3 O4 by a margin of 70 mV. Co3- x Pdx O4 catalysts provide stable catalytic performance for 450 h at 200 mA cm-2 and 20 h at 1 A cm-2 in neutral seawater. Experimental studies and theoretical calculations suggest that the incorporation of SPA cations accelerates the rate-determining water dissociation step in neutral OER pathway, and control studies rule out the provision of additional OER sites as a main factor herein.
Keywords: cobalt oxide; neutral seawater splitting; oxygen evolution reaction; strong-proton-adsorption effect.
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