A highly mismatched NiO₂-to-Pd hetero-structure as an efficient nanocatalyst for the hydrogen evolution reaction

Efficient generation of hydrogen from water is a key enabling technology towards alternative power generation sources. In this context, search for highly active and low-cost nanocatalysts (NCs) for the hydrogen evolution reaction (HER) is a crucial endeavour. In the present study, bimetallic NiPd with a novel epitaxial structure of tetrahedral symmetric Ni oxide (NiO_T) to metallic Pd contact (denoted as NiPd-CNT) has been fabricated on a carbon nanotube (CNT) supportviaa wet chemical reduction method to boost HER kinetics in an acidic medium (0.5 M H₂SO₄). This unique structure exhibits superior catalytic activity towards the HER with a significantly lower overpotential of 46 mV (at a current density of 10 mA cm⁻²). Moreover, the NiPd-CNT NC showed a low Tafel slope of 38.0 mV dec⁻¹. The overpotential and Tafel slope values are 50 mV and 22.18 mV dec⁻¹lower, respectively, as compared to those of the standard Pd-CNT NC and very close to the those of the commercial J.M.-Pt/C (30 wt% Pt) NC (overpotential is 44 mV@10 mA cm⁻²and the Tafel slope is 30.2 mV dec⁻¹). Of special relevance, the as-prepared NiPd-CNT NC exhibits nearly ∼95% stability when operated for 1000 cycles. Such a competitive HER performance is attributed to the formation of active sites on the catalyst surface due to strong lattice mismatch and electronegativity difference (χ_Pd>χ_Ni) at the heterogonous binary interface of NiO₂and Pd nanocrystals. In light of the competitive activity as compared to that of commercial J.M.-Pt/C with low cost, Pd-based bimetallic NCs can serve as a promising alternative to Pt for seizing the market.