Surface and Interface Engineering: Molybdenum Carbide-Based Nanomaterials for Electrochemical Energy Conversion.

Molybdenum carbide (Mox C)-based nanomaterials have shown competitive performances for energy conversion applications based on their unique physicochemical properties. A large surface area and proper surface atomic configuration are essential to explore potentiality of Mox C in electrochemical applications. Although considerable efforts are made on the development of advanced Mox C-based catalysts for energy conversion with high efficiency and stability, some urgent issues, such as low electronic conductivity, low catalytic efficiency, and structural instability, have to be resolved in accordance with their application environments. Surface and interface engineering have shown bright prospects to construct highly efficient Mox C-based electrocatalysts for energy conversion including the hydrogen evolution reaction, oxygen evolution reaction, nitrogen reduction reaction, and carbon dioxide reduction reaction. In this Review, the recent progresses in terms of surface and interface engineering of Mox C-based electrocatalytic materials are summarized, including the increased number of active sites by decreasing the particle size or introducing porous or hierarchical structures and surface modification by introducing heteroatom(s), defects, carbon materials, and others electronic conductive species. Finally, the challenges and prospects for energy conversion on Mox C-based nanomaterials are discussed in terms of key performance parameters for the catalytic performance.

Arrayed metal phosphide heterostructure by Fe doping for robust overall water splitting.

Transition metal phosphides (TMPs) show promise in water electrolysis due to their electronic structures, which activate hydrogen/oxygen reaction intermediates. However, TMPs face limitations in catalytic efficiency due to insufficient active sites, poor conductivity, and multiple intermediate steps in water electrolysis. Here, we synthesize a highly efficient bifunctional self-supported electrocatalyst, which consists of an N-doped carbon shell anchored on Fe-doped CoP/Co2P arrays on nickel foam (NC@Fe-CoxP/NF) using hydrothermal and phosphorization techniques. Experimental and theoretical results indicate that the modified morphology, with increased active site density and a tunable electronic structure induced by Fe doping in the CoP/Co2P heterostructure, leads to superior water electrolysis performance. The resulting NC@Fe0.1-CoP/Co2P/NF catalyst exhibits overpotentials of 122 mV for the hydrogen evolution reaction (HER) and 270 mV for the oxygen evolution reaction (OER) at 100 mA cm-2. Furthermore, using NC@Fe0.1-CoP/Co2P/NF as both the cathode and anode in an alkaline electrolyzer enables the cell system to achieve 100 mA cm-2 at a voltage of 1.70 V, while maintaining long-term catalytic durability. This work may pave the way for designing self-supported, highly efficient electrocatalysts for practical water electrolysis applications.