Zr doping Co3O4 nanowires mediated adsorption of chloridion for efficient natural seawater electrolysis.

Abstract

Natural seawater electrolysis is emerging as a desirable approach for hydrogen production, but it suffers from long-term instability due to severe chloride corrosion. In this study, Zr doped Co₃O₄ is proposed for natural seawater oxidation, which requires an overpotential of only 570 mV to drive a current density of 100 mA cm^-2, and a sustained natural seawater electrolysis at 10 mA cm^-2 for 500h exhibits only 0.78 % decay. For practicability, membrane electrode with a self-developed anion exchange membrane is assembled for overall natural seawater electrolysis, and the produced hydrogen is converted to ammonia for storage by coupling nitrate reduction. Density functional theory (DFT) calculations further reveal Zr replacing an octahedral Co atom introduces four energy levels within the gap and the lower conduction band energy is formed by substituting a tetrahedral Co atom. The highest energy barrier of the second dehydrogenation step (*OH to *O) reaches 1.82 eV and it is slightly reduced to 1.79 eV after Co₃O₄ is transformed to CoOOH. Zr-adsorbed chloridion sharply increases its absorption energy on Co sites to a positive value of 0.27 eV, which effectively protects Co active sites from chloride attack.