High-Performance and Durable Pd₅P₂/PdP₂ Heterointerface for All-pH Hydrogen Evolution Reactions

Palladium (Pd) phosphides are considered a kind of highly promising catalytic material as a Pt alternative for the hydrogen evolution reaction (HER). However, well-studied Pd phosphide catalysts still suffer from sluggish HER kinetics because of the inappropriate adsorption strengths of hydrogen and water. Herein, we synthesized a kind of Pd5P2/PdP2 heterogeneous nanoparticle catalyst with a good HER performance in both acidic (η10 = 28 mV, η500 = 150 mV) and alkaline electrolytes (η10 = 31.2 mV, η500 = 180 mV). Moreover, Pd5P2/PdP2@CNTs exhibit a low Tafel slope value of 24.3 mV dec–1 and a high turnover frequency value of 38.9 s–1 at 100 mV in 0.5 M H2SO4, which are one of the best catalysts for HER in the reported state-of-the-art noble metal-based electrocatalysts. In addition, the flow-type water electrolyzers [PdP2/Pd5P2@CNTs(−)||S–NiFe-LDH(+)] and [PdP2/Pd5P2@CNTs(−)||IrO2(+)] were operated successfully with a low cell voltage of 1.71 and 1.75 V at 75 °C, respectively, in acidic and alkaline electrolytes, which can also be driven by a solar cell cart without additional energy applied, even at an industrial current density of 500 mA cm–2. In situ Raman and temperature-programmed desorption experiments demonstrate that the moderate H2O absorption strength and faster H2 desorption kinetics on the PdP2/Pd5P2 heterojunction promote water dissociation and the release of H2, thereby improving its HER performance. This work highlights a heterogeneous interface modulation design principle, which may inspire the development of more advanced HER catalysts.