Sulfur doping induces internal polarization field in NiFe-LDH for bifunctioanl HER/OER and overall water/simulated seawater splitting

With the development of renewable energy technologies, electrochemical water splitting has been proven to be an effective strategy for energy conversion. Especially, exploring a bifunctional material for electrochemical water splitting devices is vital. Herein, a bifunctional sulfur-doped NiFe-LDH (NFS) through one-step chemical oxidation-assisted etching route was successfully synthesized at room temperature. Moreover, the effects of the component of the etching solution and etching time on the catalytic performance were systematically investigated, so as to explore the optimal synthetic route. The resulted NFS catalyst depicted obvious nanosheets based 3D open structure, which was demonstrated to provide abundant electrochemical active sites, facilitate the rapid diffusion of ions and improve the electrical conductivity as well as the catalytic stability. Electrochemical tests showed that the overpotential of the as-prepared catalyst was 256 mV for OER and 171 mV for HER at 10 mA cm-2 in 1 M KOH solution, which exhibited excellent bifunctional activity. Furthermore, the electrolyzer was assembled using as-prepared catalyst as both the anode and cathode, which expressed good stability either in 1 M KOH (1.67 V@10 mA cm-2) or in alkaline simulated seawater (1.84 V@10 mA cm-2). To better elucidate the crucial role of sulfur doping in the NFS catalyst to boost HER and OER, both theory and poisoning experiment had been proceeded and verified. All in all, the NFS catalyst with excellent bifunctional activity was synthesized by one-step chemical oxidation-assisted etching route at room temperature, which was promising as candidate to be used in commercial water splitting.