Achieving the optimal Ni(OH)2 : Pt ratio for enhancing electrocatalytic water-dissociation and H2 delivery in proton-deficient environments

Abstract

Despite the availability of abundant, inexpensive non-noble metal-based anode catalysts for alkaline water electrolysis, the cathodic hydrogen evolution reaction (HER) continues to be a challenge, even in the case of state-of-the-art Pt catalysts. In such proton-deficient environments, a metal hydroxide-/oxide-based co-catalyst that can help polarize the H–O bond in water has been found to promote proton abstraction and subsequent reduction into H₂ on Pt and Ru surfaces. In this regard, the Ni(OH)₂ : Pt co-catalyst is one of the best. However, the relationship between the ratio of Ni(OH)₂ and Pt and the alkaline HER is not well-understood, although it is essential for further advancements. Herein, we report the results of a systematic study aimed at gradually increasing the Ni(OH)₂ : Pt ratio and studying the physical, chemical, and electrochemical properties of the catalyst, which led us to achieve the perfect balance between Ni(OH)₂ and Pt. The optimised Ni(OH)₂ : Pt-3 catalyst with a Pt to Ni(OH)₂ ratio of 3.3 atom% outperformed commercial Pt/C (20 wt%) by requiring only 9 and 50 mV for −10 and −100 mA cm⁻², respectively, and exhibited faster kinetics with a very low Tafel slope of 40 mV dec⁻¹, which is an impressive feat in a proton-deficient pH of 14. Thus, this study provides new insights into the role of the ratio of Ni(OH)₂ and Pt in alkaline HERs.