Strong-Proton-Adsorption Co-Based Electrocatalysts Achieve Active and Stable Neutral Seawater Splitting

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 (approximate to 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-xPdxO4) catalysts. These achieve an OER overpotential of 370 mV at 10 mA cm(-2) in pH-neutral simulated seawater, outperforming Co3O4 by a margin of 70 mV. Co3-xPdxO4 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.

Automated summary

Direct electrolysis of pH-neutral seawater to generate hydrogen faces an anodic competition issue between the chlorine evolution and the oxygen evolution reaction (OER), resulting in low current density and limited operating stability. In this study, a proton-adsorption-promoting strategy has been proposed to increase the OER rate, allowing for enhanced and stable neutral seawater splitting. Palladium-doped cobalt oxide (Co3-xPdxO4) catalysts exhibit the best performance with an OER overpotential of 370 mV at 10 mA cm(-2) in pH-neutral simulated seawater, outperforming Co3O4 by 70 mV. Co3-xPdxO4 catalysts also demonstrate long-term stability in neutral seawater, with 450 hours at 200 mA cm(-2) and 20 hours at 1 A cm(-2). Experimental and theoretical analyses suggest that the inclusion of SPA cations accelerates the rate-determining water dissociation step in the neutral OER pathway, while ruling out additional OER sites as a main factor.