Electrocatalytic water splitting is a green and sustainable means of hydrogen production. However, the widespread application of water splitting technology will lead to a large consumption of fresh water, which will undoubtedly increase the cost of hydrogen production. Recently, the production of H2 through seawater electrolysis has attracted attention, and more and more research efforts are pushing this technology closer to practical applications. It is important to note that chloride ions (Cl) and their derivatives (e.g., hypochlorite) in seawater will continuously and actively corrode the electrode during the oxidation of seawater, resulting in rapid deactivation of the catalyst. The alkaline seawater makes the thermodynamic potential of OER about 480 mV lower than that of chloride ions, which means that a sufficiently high water oxidation activity can directly limit the conversion of Cl to reactive chlorine derivatives.
However, at high currents, the overpotential of most OER catalysts in alkaline seawater exceeds 480 mV, which is not conducive to the realization of industrial-grade seawater electrolysis for hydrogen production. Therefore, the exploration of catalysts that can maintain high OER activity and well inhibit chlorine-related reactions at industrial-grade current density is the key to promote the practical application of seawater electrolysis.
Recently,Tang Bo, Shandong Normal UniversitySun XupingGong Feng, Southeast UniversitywithWang Yan, University of Electronic Science and Technology of ChinaAn adaptive catalyst ((NiFe)C2O4 NF) can achieve in-situ carboxyl anion self-conversion (cost, from C2O22 to CO32) to inhibit the adsorption of Cl by materials.
In-situ non-situ spectroscopy studies showed that the cost of (NiFe)C2O4 NF induced the preferential adsorption of self-released CO32 on the surface of the catalyst, effectively rejecting Cl. At the same time, this spontaneous cost is relatively stable during long-term alkaline seawater oxidation (ASO): the CO32 to C2O22 ratio (from 300 to 600 hours) and the ratio of C2O22 to CO32 to total carbon fluctuate less. What's more, this cost also accelerates the conversion of the material into disordered NiOOH, which promotes OER activity while ensuring that the material is not corroded by CL.
Therefore, the prepared (NiFe)C2O4 NF catalyst exhibits excellent activity against ASO, with an overpotential of only 349 mV at a current density of 1 A cm2, which is better than most previously reported catalysts. In addition, (NiFe)C2O4 NF operates continuously for 600 hours at a current density of 1 Acm2 with negligible activity attenuation.
It is worth noting that in the asymmetric alkaline seawater PEM system, the Faraday efficiency of H2 produced by (NiFe)C2O4 NF is about 100%, showing great potential for practical applications. Overall, this study not only provides an effective catalyst surface design concept, but also provides an idea for protecting the active site (prolonging the lifetime) of Ni-based catalyst ** state metal in electrolytic alkaline seawater-H2 conversion system.
carbon oxyanion self-transformation on nife oxalates enables long-term ampere-level current density seawater oxidation. angewandte chemie international edition, 2023. doi: 10.1002/anie.202316522