Regulating the Electronic States of NiSe2 by Cr-doping to Promote Formation of Active Phase for High Catalytic Performance of Urea Oxidation Reaction

Abstract

At present, urea oxidation reaction (UOR), as a small molecule oxidation reaction, can replace anodic oxygen evolution reaction (OER) and has become a research hotspot in the field of efficient and economical hydrogen production through water electrolysis. However, the kinetics of UOR is still slow compared to hydrogen evolution reaction (HER) and involves the adsorption and desorption of various intermediates. It is essential to develop efficient and stable UOR catalysts. In this paper, Cr-doped NiSe2 (Cr0.25-NiSe2) was synthesized as high-performance catalyst for UOR by hydrothermal and selenization methods. The doping of Cr in NiSe2 can regulate electron distribution of Ni, weaken the adsorption of intermediates on NiSe2, and accelerates the reaction kinetics of UOR. In-situ Raman tests show that Cr doping is conducive to surface reconstruction of NiSe2, and the crystalline NiOOH with high catalytic activity is generated at a low potential, which is helpful to improve the performance. In addition, the strong electron absorption ability of the Cr6+ generated by partial oxidation of Cr3+ ions during the UOR can effectively stabilize high valence active sites of the catalyst. Based on the above advantages, the prepared Cr0.25-NiSe2 as a catalyst for UOR only requires a potential of 1.37 V vs. RHE at 100 mA cm-2 in 1.0 M KOH+0.33 M urea solution, with an overpotential negative shift of 270 mV compared to OER. Furthermore,the Cr0.25-NiSe2 showed excellent catalytic stability for UOR, with a catalytic activity retention of 96.8% after 100 h of cyclic testing at 10 mA cm-2.