Phosphide

Abstract: Electrochemical production of hydrogen from water has been directed to the search for non-noble metal based and earth-abundant catalysts. In this work, we propose a novel cost-effective catalyst, molybdenum phosphide that exhibits high activity towards the hydrogen evolution reaction (HER) in both acid and alkaline media even in bulk form. Comparative analysis of Mo, Mo3P and MoP as catalysts for HER clearly indicates that phosphorization can potentially modify the properties of the metal and different degrees of phosphorization lead to distinct activities and stabilities. Theoretical calculations by density functional theory also show that a simple phosphorization of molybdenum to form MoP introduces a good ‘H delivery’ system which attains nearly zero binding to H at a certain H coverage. With the combination of experimental results and theoretical calculations, this work has enlightened a new way of exploring cost-effective catalysts for HER.

Abstract: Introducing sulfur into the surface of molybdenum phosphide (MoP) produces a molybdenum phosphosulfide (MoP|S) catalyst with superb activity and stability for the hydrogen evolution reaction (HER) in acidic environments. The MoP|S catalyst reported herein exhibits one of the highest HER activities of any non-noble-metal electrocatalyst investigated in strong acid, while remaining perfectly stable in accelerated durability testing. Whereas mixed-metal alloy catalysts are well-known, MoP|S represents a more uncommon mixed-anion catalyst where synergistic effects between sulfur and phosphorus produce a high-surface-area electrode that is more active than those based on either the pure sulfide or the pure phosphide. The extraordinarily high activity and stability of this catalyst open up avenues to replace platinum in technologies relevant to renewable energies, such as proton exchange membrane (PEM) electrolyzers and solar photoelectrochemical (PEC) water-splitting cells.

Abstract: Hollow nanostructures have attracted increasing research interest in electrochemical energy storage and conversion owing to their unique structural features. However, the synthesis of hollow nanostructured metal phosphides, especially nonspherical hollow nanostructures, is rarely reported. Herein, we develop a metal-organic framework (MOF)-based strategy to synthesize carbon incorporated Ni-Co mixed metal phosphide nanoboxes (denoted as NiCoP/C). The oxygen evolution reaction (OER) is selected as a demonstration to investigate the electrochemical performance of the NiCoP/C nanoboxes. For comparison, Ni-Co layered double hydroxide (Ni-Co LDH) and Ni-Co mixed metal phosphide (denoted as NiCoP) nanoboxes have also been synthesized. Benefiting from their structural and compositional merits, the as-synthesized NiCoP/C nanoboxes exhibit excellent electrocatalytic activity and long-term stability for OER.

Abstract: Hydrogen evolution by means of electrocatalytic water-splitting is pivotal for efficient and economical production of hydrogen, which relies on the development of inexpensive, highly active catalysts. In addition to sulfides, the search for non-noble metal catalysts has been mainly directed at phosphides due to the superb activity of phosphides for hydrogen evolution reaction (HER) and their low-cost considering the abundance of the non-noble constituents of phosphides. Here, recent research focusing on phosphides is summarized based on their synthetic methodology. A comparative study of the catalytic activity of different phosphides towards HER is then conducted. The catalytic activity is evaluated by overpotentials at fixed current density, Tafel slope, turnover frequency, and the Gibbs free energy of hydrogen adsorption. Based on the methods discussed, perspectives for the various methods of phosphides synthesis are given, and the origins of the high activity and the role of phosphorus on the improved activity towards HER are discussed.