Cobalt Phosphide Single Site Electrocatalysts derived from 2D ZIF-8 for Hydrogen Evolution Reaction

Hydrogen (H2) is a promising energy carrier due to its high gravimetric energy density and environmental friendliness. Among different approaches of H2 production, hydrogen evolution reaction (HER) via electrochemical water splitting has attracted significant research interests when electricity can be supplied by sustainable energy sources, such as solar, wind, and tidal energy. Electrocatalysts play a crucial role in accelerating HER's kinetics. Platinum (Pt)-based electrocatalysts have excellent catalytic activities for HER due to their optimal adsorption/desorption energy for hydrogen and have been are widely used in industrial water electrolyzers. However, their high cost and poor stability seriously limit their broad adoption. Tremendous research efforts have been devoted to developing electrocatalysts based on earth-abundant transition metals, such as iron (Fe), cobalt (Co), nickel (Ni), and molybdenum (Mo). In this regard, emerging single-atom catalysts (SACs) with maximum atom utilization is considered as one of the most promising solutions. Here, a new cobalt phosphide single site HER electrocatalyst was synthesized from ultrathin 2D ZIF-8 metal-organic framework (MOF) nanosheets using a mixed solution containing Zn2+, Co2+, 2-methylimidazole. The 2D MOF nanosheets facilitate the phosphating of single atom Co sites rather than forming cobalt phosphide nanoparticles. Structural characterizations indicated that the as-synthesized electrocatalyst (denoted as CoPSS) has a CoN2P2 coordination structure, where Co metal centres coordinate with two P atoms and two N atoms. CoPSS demonstrates an excellent HER performance in an alkaline electrolyte with an overpotential of 117 mV at 10 mA cm-2 and a Tafel slope of 55 mV dec-1. This work provides a facile and cost-effective strategy for preparing high efficient HER electrocatalysts