Surface‐Dependent Intermediate Adsorption Modulation on Iridium‐Modified Black Phosphorus Electrocatalysts for Efficient pH‐Universal Water Splitting

2D black phosphorus (BP) is one promising electrocatalyst toward hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) catalysis. The too strong adsorption of oxygen intermediates during OER, while the too weak adsorption of hydrogen intermediate during HER, however, greatly compromise its practical water splitting applications with overpotentials as high as 450 mV for OER and 420 mV for HER to achieve 10 mA cm−2 under alkaline conditions. Herein, by rationally introducing the nanosized iridium (Ir) modifier together with optimized exposing surface toward electrolytes, an efficient Ir‐modified BP electrocatalyst with much favorable adsorption energies toward catalytic intermediates possesses an outstanding pH‐universal water splitting performance, surpassing the nearly all reported BP‐based catalysts and the commercial noble‐metal catalysts. The Ir‐modified BP catalyst with the optimized exposed surfaces only requires an overall cell voltage of 1.54 and 1.57 V to achieve 10 mA cm−2 in acidic and alkaline electrolysers, respectively. This design uncovers the potential applications of 2D BP in practical electrocatalysis fields via decreasing reaction intermediate adsorption energy barriers and promoting the interfacial electron coupling for heterostructured catalysts, and offers new insights into the surface‐dependent activity enhancement mechanism. An efficient iridium‐modified 2D black phosphorus electrocatalyst is rationally designed to achieve the desired adsorption energies toward catalytic intermediates, and the resultant catalyst demonstrates outstanding pH‐universal water splitting performances, surpassing the commercially dominating catalysts. Furthermore, an interesting surface‐dependent activity enhancement mechanism is identified.