Extremely efficient and stable hydrogen evolution by a Pt/NiOx composite film deposited on a nickel foam using a mixed metal-imidazole casting method

Abstract

Development of efficient and robust electrocatalysts for the hydrogen evolution reaction (HER) is of great importance for H₂ production via water splitting which is one of the most promising sustainable and eco-friendly approaches for H₂ production with zero CO₂ emission. Herein we report a Pt/NiO_x composite film deposited on a nickel foam (NF) electrode via a mixed metal-imidazole casting (MiMIC) method using a precursor suspension containing H₂PtCl₆ in mixed solvents of methanol/1-methylimidazole (MeIm) (3 : 1). The Pt/NiO_x composite film (denoted as Pt-film(w)) was fully characterized by possible spectroscopic techniques, compared with the Pt-deposited film (denoted as Pt-film(w/o)) prepared without MeIm in a similar manner. Pt-film(w) is composed of well-dispersed Pt nanoparticles incorporated into the co-deposited NiO_x layer on the NF surface, in sharp contrast with Pt nanoparticles mostly formed as an elongated cluster into the deposited layer for Pt-film(w/o). X-ray photoelectron spectroscopic (XPS) data indicate the single state of Pt^IV on the surface of Pt-film(w) but the mixed state of Pt^IV and Pt⁰ on the Pt-film(w/o) surface. Presumably, the Pt^IV state of the Pt nanoparticle surface is stabilized due to interaction with nickel oxoes of the NiO_x layer for both films. Pt-film(w) showed extremely efficient HER performance with the lowest overpotentials of only η¹⁰ = 4.2 and η¹⁰⁰ = 27 mV among the state-of-the-art HER electrocatalysts under alkaline conditions, so far. The mass activity (0.42 A cm⁻² mg_Pt⁻¹) of Pt-film(w) at η = 50 mV is 60 times higher than that of the commercial 10 wt% Pt/C film on the NF electrode as a commonly used HER electrocatalyst. The extremely stable HER electrocatalysis was first demonstrated at a high current density of −100 mA cm⁻² for 60 h under alkaline conditions. This study opens up a new avenue towards practical application of Pt-film(w) as an efficient HER cathode to large-scale and commercial systems for water splitting.