Carbide Supported Phosphides Are Superior Electrocatalysts for Hydrogen Generation Than Nanocrystalline Phosphides

Abstract

Phosphides such as hexagonal nickel phosphide (Ni2P) and carbides such as hexagonal Fe2N type molybdenum carbide (Mo2C) have been extensively explored as efficient and stable hydrogen evolution reaction (HER) catalysts in both acid and base electrolytes. To a lesser extent, they have also been investigated as oxygen evolution reaction (OER) catalysts in alkaline medium in recent years. Molybdenum carbide has been shown to exhibit superior enhancement in the electrochemical activity compared to carbon materials as support for noble metal catalysts such as platinum. It has also been shown that carbon support deposited phosphides show enhanced HER and OER activities compared to nanocrystalline phosphide powders. Thus, a carbide supported nickel phosphide should show relatively enhanced electrocatalytic activities than carbon supported material as well as unsupported crystalline powders. While the two families of materials have been investigated individually, to our knowledge, there is not a report of a composite material of phosphide and carbide. Since both phosphide and carbides can form hexagonal crystal structure there is likelihood that some phosphides can be deposited on molybdenum carbide surfaces. The electrocatalytic activities of phosphides and carbides depend on the optimal adsorption and desorption energies of hydrogen and hydrogen ion species for the reaction to proceed efficiently. Formation of composite electrocatalysts is postulated to give rise to superior catalyst sites. This presentation will investigate the structural and catalytic activities of transition metal phosphide deposited on carbothermic reduction derived molybdenum carbide. Additionally, intermetallic interactions and electrochemical stabilities of the composite catalysts will be discussed.