Influence of metal-organic framework structure on the electrocatalytic activity of nickel phosphide nanoparticles synthesized from solvothermal phosphidization

Transition metal phosphides find applications in energy storage and electrocatalysis. Understanding the influence of precursor structure to the electrocatalytic activity is essential in aiding the further design of metal phosphides. Here, nickel phosphide nanoparticles (Ni2P) are synthesized by solvothermal phosphidization, where metal-organic framework (MOF) precursors are reacted with white phosphorus. The 1,4-dicarboxybenzene, 2,6-naphthalenedicarboxylic acid and 4,4'-biphenyldicarboxylic acid are utilized as the ligand to prepare MOF. The size of the crystalline Ni2P is affected by the ligand of the MOF. Carbon cloth (CC) is used as the substrate to investigate the oxygen evolution reaction activity (OER) of the Ni2P. The Ni2P/CC synthesized with 1,4-dicarboxybenzene as the MOF ligand exhibits the highest OER activity in 1 M KOH, with 335 mV overpotentials to reach 10 mA cm-2. The high OER activity is originated from higher number of active sites, and improved intrinsic activity, as demonstrated from the lower Tafel slope value and lower charge transfer resistance. Lattice oxygen evolution mechanism is involved, and the adsorption energy of hydroxyl groups is optimized. The Ni2P/CC are stable towards the long-term OER in aqueous alkaline solutions, and the crystalline Ni2P phase disappears after the long-term test. This study could aid the further design of metal phosphide nanostructures synthesized using solvothermal phosphidization method to electrocatalyze OER.