Hydrogen is a fuel with a potentially zero-carbon footprint viewed as a viable alternative to fossil fuels. It can be produced in a large scale via electrochemical water splitting using electricity derived from renewable sources, but this would require highly active, inexpensive, and stable hydrogen evolution reaction (HER) catalysts to replace the Pt benchmark. Transition-metal phosphides (TMPs) are potential Pt replacements owing to their generally high activity as well as versatility as HER catalysts for different pH media. This review summarizes the recent progress in the development of TMP HER electrocatalysts, focusing on the strategies that have been recently explored to tune the activity in acidic, neutral, and basic media. These strategies are the doping of TMPs with metal and nonmetal elements, fabrication of multimetallic phosphide phases, and construction of multicomponent heterostructures comprising TMPs and another component such as a different TMP or a metal oxide/hydroxide. The synthetic methods utilized to design the catalysts are also presented. Finally, the challenges still remaining and future research directions are discussed.

To arrive to sustainable hydrogen‐based energy solutions, the understanding of water‐splitting catalysts plays the most crucial role. Herein, state‐of‐the‐art hypotheses are combined on electrocatalytic active metal sites toward the oxygen evolution reaction (OER) to develop a highly efficient catalyst based on Earth‐abundant cobalt and zinc oxides. The precursor catalyst Zn0.35Co0.65O is synthesized via a fast microwave‐assisted approach at low temperatures. Subsequently, it transforms in situ from the wurtzite structure to the layered γ‐Co(O)OH, while most of its zinc leaches out. This material shows outstanding catalytic performance and stability toward the OER in 1 m KOH (overpotential at 10 mA cm−2 ηinitial = 306 mV, η98 h = 318 mV). By comparing the electrochemical results and ex situ analyses to today's literature, clear structure‐activity correlations are able to be identified. The findings suggest that coordinately unsaturated cobalt octahedra on the surface are indeed the active centers for the OER.

Nanocomposites made of stacked‐cup carbon nanotubes coated with NiO (NiO/SCCNTs) via atomic layer deposition (ALD) were synthesized in order to obtain a material exhibiting enhanced and optimized electrochemical performance towards detections of glucose. The structure and morphology were characterized by transmission electron microscopy (TEM) and X‐ray diffraction (XRD). NiO deposited as nanocrystalline particles in the cubic modification, were well dispersed and directly anchored on SCCNTs forming a smooth particulate thin film, which becomes more dense with the increase of the number of ALD cycles. The NiO/SCCNTs samples with various thicknesses of the NiO coating (0.8 nm, 1.7 nm, 4.0 nm, 6.5 nm, 14.0 nm and 21.8 nm) were applied for enzyme‐free glucose sensing. Their electrochemical performance strongly depends on the thickness of the deposited NiO thin film. The best performing glucose sensors respond over a wide concentration range from 2 μM to 2.2 mM (R2=0.9979) with remarkably enhanced sensitivity (1252.3 μA cm−2 mM−1), with a limit of detection (LOD) of 0.10 μM (S/N=3) and with a fast response time (lower than 2 s). The significant performance improvement can be attributed to the conformal NiO coating, high surface to volume ratio and to the optimized thickness of the NiO thin film. The advantage of our sensors is also associated with the conductive supporting material (SCCNTs), simplicity of fabrication, high sensitivity, selectivity, stability and reproducibility for the rapid quantification of glucose.

Coordination polymers (CPs) and metal–organic frameworks (MOFs) have emerged as versatile precursors for transition-metal phosphides catalysts. However, the controlled synthesis of CPs-derived bimetallic phosphides remains a challenge, as mixtures of various phosphide phases are often formed. Here, it is shown that controlling the formation of pure CoMoP and CoMoP2 nanoparticles requires a careful choice of the ligands used to construct the precursors based on the chemical properties of the metals. In particular, the nature and number of the coordination moieties of the ligand play key roles. CoMoP and CoMoP2 particles coated with N-doped carbon were derived from phosphonate-based CPs and compared as hydrogen evolution reaction (HER) electrocatalysts in acidic medium. CoMoP2 is more active and shows a turnover frequency (TOF) of 0.9 s–1 compared to 0.4 s–1 for CoMoP. The higher intrinsic activity of the CoMoP2 catalytic sites correlates with the differences in the electronic structure of the materials, with a larger charge transfer from the molybdenum to the phosphorus found for CoMoP2.