Hydrogen oxidation and oxygen reduction reactions on palladium nano-electrocatalyst supported on nickel-deficient MOF-derived carbons

Abstract

Pd/Ni-based catalysts consisting of Ni-rich MOF-derived carbon (Pd/Ni-r/MOFDC) and Ni-deficient counterpart (Pd/Ni-d/MOFDC) have been demonstrated as efficient nanostructured catalysts for alkaline hydrogen oxidation (HOR) and oxygen reduction reactions (ORR). Physico-chemical analysis of the catalysts unravels the significance of controlled chemical etching of the Ni-based MOFDC prior to deposition of Pd catalyst, thereby controlling the level of Ni(OH)2 interface and defects or oxygen vacancies. The Pd/Ni-d/MOFDC exhibits excellent performance towards HOR compared to the Pd/Ni-r/MOFDC in respects of decreased onset potential (Eonset), but increased exchange current density (jo.s), heterogeneous rate constant (k0), kinetic current (jK), diffusion coefficient (D) and mass activity (jo.m). The more facile HOR performance on Pd/Ni-d/MOFDC corroborates its reduced activation energy (EA) by a factor of 1/3. The alkaline HOR follows the Heyrovsky-Volmer and Tafel-Volmer processes on Pd/Ni-r/MOFDC and Pd/Ni-d/MOFDC, accordingly, evident by their Tafel slope (ba) values. The Pd/Ni-d/MOFDC equally shows improved ORR activity compared to the Pd/Ni-r/MOFDC. Density functional theory (DFT) calculations agree with the experimental data, especially the contributory effects of the chemically etched composite support. Pd/Ni-d/MOFDC promises to be a viable electrocatalyst for the development of alkaline membrane fuel cells (AMFCs).