Modified Pd–HPMo@GNP as a highly effective electro-/nanocatalyst for the hydrogen evolution reaction and 4-nitrophenol reduction

Abstract

In light of current energy conversion paradigms, this study discusses the urgent need for the effective organic pollution reduction and sustainable hydrogen production. The aim of this work is to fabricate precise nanocatalysts and to investigate water electrolysis with the objective of enhancing the kinetics of the hydrogen evolution process (HER). This work examines Pd and phosphomolybdic acid (HPMo) as modified electrocatalysts after they were immobilized on graphene nanosheets using a two-step wet chemical procedure. The resulting Pd–HPMo@GNP nanocomposite exhibited excellent catalytic performance, as validated through various analytical techniques. According to electrochemical investigation, Pd–HPMo@GNP performed better in the HER than the benchmark HER catalyst Pt/C, which is commercially available. It displayed a low overpotential of 94 mV vs. RHE (at 10 mA cm⁻² current density); a low Tafel slope of 90 mV dec⁻¹, indicating fast electron transfer kinetics; robust stability during prolonged chronoamperometric studies for 24 h; and high turnover frequency (TOF) value of 1.397 × 10⁻⁴ s⁻¹, indicating the existence of more active sites for the generation of H₂ molecules in the acidic electrolytic medium (0.5 M H₂SO₄). Further, the synthesized Pd–HPMo and Pd–HPMo@GNP nanocomposites were efficient towards catalytic 4-nitrophenol reduction in a water medium in the presence of NaBH₄, i.e., 50 mL of 0.43 mM 4-nitrophenol was reduced to 4-aminophenol in 2 minutes and 7 minutes, respectively, thus showcasing their potential in environmental applications. In general, this work advances the development of sustainable catalysts for hydrogen generation and pollutant remediation.