Self-supported ternary (NixFey)2P nanoplates arrays as an efficient bifunctional electrocatalyst for overall water splitting

A Review of Transition Metal Boride, Carbide, Pnictide, and Chalcogenide Water Oxidation Electrocatalysts

Transition metal borides, carbides, pnictides, and chalcogenides (X-ides) have emerged as a class of materials for the oxygen evolution reaction (OER). Because of their high earth abundance, electrical conductivity, and OER performance, these electrocatalysts have the potential to enable the practical application of green energy conversion and storage. Under OER potentials, X-ide electrocatalysts demonstrate various degrees of oxidation resistance due to their differences in chemical composition, crystal structure, and morphology. Depending on their resistance to oxidation, these catalysts will fall into one of three post-OER electrocatalyst categories: fully oxidized oxide/(oxy)hydroxide material, partially oxidized core@shell structure, and unoxidized material. In the past ten years (from 2013 to 2022), over 890 peer-reviewed research papers have focused on X-ide OER electrocatalysts. Previous review papers have provided limited conclusions and have omitted the significance of "catalytically active sites/species/phases" in X-ide OER electrocatalysts. In this review, a comprehensive summary of (i) experimental parameters (e.g., substrates, electrocatalyst loading amounts, geometric overpotentials, Tafel slopes, etc.) and (ii) electrochemical stability tests and post-analyses in X-ide OER electrocatalyst publications from 2013 to 2022 is provided. Both mono and polyanion X-ides are discussed and classified with respect to their material transformation during the OER. Special analytical techniques employed to study X-ide reconstruction are also evaluated. Additionally, future challenges and questions yet to be answered are provided in each section. This review aims to provide researchers with a toolkit to approach X-ide OER electrocatalyst research and to showcase necessary avenues for future investigation.

Stoichiometry design in hierarchical CoNiFe phosphide for highly efficient water oxidation

Rational composition design of trimetallic phosphide catalysts is of significant importance for enhanced surface reaction and efficient catalytic performance. Herein, hierarchical Co _x Ni _y Fe _z P with precise control of stoichiometric metallic elements (x:y:z = (1-10):(1-10):1) has been synthesized, and Co_1.3Ni_0.5Fe_0.2P, as the most optimal composition, exhibits remarkable catalytic activity (η = 320 mV at 10 mA cm^-2) and long-term stability (ignorable decrease after 10 h continuous test at the current density of 10 mA cm^-2) toward oxygen evolution reaction (OER). It is found that the surface P in Co_1.3Ni_0.5Fe_0.2P was replaced by O under the OER process. The density function theory calculations before and after long-term stability tests suggest the clear increasing of the density of states near the Fermi level of Co_1.3Ni_0.5Fe_0.2P/Co_1.3Ni_0.5Fe_0.2O, which could enhance the OH^- adsorption of our electrocatalysts and the corresponding OER performance.

ELECTRONIC SUPPLEMENTARY MATERIAL

Supplementary material is available in the online version of this article at 10.1007/s40843-022-2061-x.

Ruthenium-nickel-cobalt alloy nanoparticles embedded in hollow carbon microtubes as a bifunctional mosaic catalyst for overall water splitting

The development of efficient bifunctional catalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is essential for reducing the cost of hydrogen production by water splitting. Herein, hollow microtubes composed of RuNi₁Co₁ alloy nanoparticles uniformly embedded in the carbon matrix (RuNi₁Co₁@CMT) are prepared through a simple impregnation followed by reduction. Benefiting from the unique mosaic structure and the synergistic effect between Ru and NiCo, RuNi₁Co₁@CMT achieves more exposed active sites and improved reaction kinetics. As a consequence, RuNi₁Co₁@CMT exhibits considerable catalytic activities with the overpotentials of 78 mV for HER and 299 mV for OER at 10 mA cm^-2 in 1 M KOH. In addition, RuNi₁Co₁@CMT exhibits excellent stability for up to 30 h in both HER and OER processes at 20 mA cm^-2, which is attributed to the protection of the RuNi₁Co₁ alloy particles by the carbon layer. Furthermore, the assembled RuNi₁Co₁@CMT || RuNi₁Co₁@CMT overall water splitting system shows a cell voltage of 1.58 V at 10 mA cm^-2. The density functional theory (DFT) calculations indicate that the addition of Ru can optimize the hydrogen adsorption free energy of Ni and Co sites. Finally, a solar panel-driven water splitting device is built, which can realize green and sustainable hydrogen production. The fabrication of RuNi₁Co₁@CMT provides a new way for the preparation of effective alloy nanomaterials for energy storage and conversion.

One-step synthesis of amorphous nickel iron phosphide hierarchical nanostructures for water electrolysis with superb stability at high current density

The development of noble-metal-free high-performance bifunctional catalysts for both the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is essential but challenging for hydrogen production from water electrolysis. Herein, amorphous bimetallic nickel-iron phosphide hierarchical nanostructures enrooted on nickel-iron alloy foam (NiFeP/NFF) are facilely fabricated via direct phosphidation of NFF at low temperature and developed as an efficient self-supporting bifunctional electrocatalyst to catalyze both the OER and HER with high activity, fast kinetics and excellent stability. Moreover, an alkaline water electrolyzer simultaneously utilizing NiFeP/NFF as the cathode and anode only needs a cell voltage of 1.58 V to afford a current density of 10 mA cm-2, overpassing most of the reported bifunctional electrocatalysts and comparable to noble metal-based ones. Impressively, the NiFeP/NFF-based symmetric electrolyzer can work well without appreciable performance degradation at a high current density of 500 mA cm-2 for over 1000 h for continuous hydrogen production with 100% faradaic efficiency, showing superb durability and great promise for industrial application.