Regulating the electronic states of NiSe2 by Cr-doping to promote formation of active phases for high catalytic performance of the urea oxidation reaction

Abstract

At present, the urea oxidation reaction (UOR), as a small molecule oxidation reaction, can replace the 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 the UOR is still slow compared to that of the 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 (Cr_0.25-NiSe₂) was synthesized as a high-performance catalyst for the 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 accelerate the reaction kinetics of the UOR. In situ Raman tests show that Cr doping is conducive to surface reconstruction of NiSe₂, and 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 Cr_0.25-NiSe₂ as a catalyst for the 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 the OER. Furthermore, Cr_0.25-NiSe₂ showed excellent catalytic stability for the UOR, with a catalytic activity retention of 96.8% after 100 h of cyclic testing at 10 mA cm⁻².