As hydrogen has been increasingly considered as promising sustainable energy supply, electrochemical overall water splitting driven by highly efficient non‐noble metal electrocatalysts has aroused extensive attention. Transition metal phosphides (TMPs) have demonstrated remarkable electrocatalytic performance, including high activity and robust durability towards hydrogen evolution reaction (HER) in acidic and alkaline as well as neutral electrolytes. In this Review, up‐to‐date progress of TMP‐based HER electrocatalysts is summarized. Various synthesis strategies of TMPs based on selected phosphorus sources are presented, and the reaction mechanisms of HER as well as the contribution of phosphorus in the TMPs to HER activity are briefly discussed. The multiscale approaches for promoting the activity and stability of TMP‐based catalysts are discussed with respect to intrinsic electronic structure, hybrids, microstructure, and working electrode interface. Some crucial issues and future perspectives of TMPs are pointed out. These modulated approaches and challenges are also instructive for constructing other high‐activity energy‐related electrocatalysts.

Ammonia (NH3) electrosynthesis from atmospheric nitrogen (N2) and water is emerging as a promising alternative to the energy‐intensive Haber–Bosch process; however, such a process is difficult to perform due to the inherent inertness of N2 molecules together with low solubility in aqueous solutions. Although many active electrocatalysts have been used to electrocatalyze the N2 reduction reaction (NRR), unsatisfactory NH3 yields and lower Faraday efficiency are still far from practical industrial production, and thus, considerable research efforts are being devoted to address these problems. Nevertheless, most reports still mainly focus on the preparation of electrocatalysts and largely ignore a summary of optimization–modification strategies for the NRR. In this review, a general introduction to the NRR mechanism is presented to provide a reasonable guide for the design of highly active catalysts. Then, four categories of NRR electrocatalysts, according to chemical compositions, are surveyed, as well as several strategies for promoting the catalytic activity and efficiency. Later, strategies for developing efficient N2 fixation systems are discussed. Finally, current challenges and future perspectives in the context of the NRR are highlighted. This review sheds some light on the development of highly efficient catalytic systems for NH3 synthesis and stimulates research interests in the unexplored, but promising, research field of the NRR.

The development of high activity and stability nonprecious metal catalysts for oxygen evolution and reduction is necessary to solve energy supply issues. Here, porous nanowire arrays composed of Co 3 O 4 nanoparticles and carbon species are prepared by a facile carbonization of the metal−organic framework materials of ZIF-67 which directly grow on Ni foam. The obtained hybrid materials possess a large surface area of 345 m 2 g −1 and a high carbon content. The hierarchically interconnected nanowire arrays with porous structure strongly immobilized on Ni foam facilitate the diffusion of generated gas, shorten electrolyte diffusion distance, and enhance charge transport. As the working electrode for oxygen evolution reaction without any extra modification in 1.0 M KOH, it can provide a stable current density of 10 mA cm −2 at 1.54 V (vs RHE), along with robust durability. Additionally, the Co 3 O 4 −C hybrid materials worked as oxygen reduction catalyst exhibit a positive onset potential of 0.91 V, large limiting current density, and excellent stability. When used as the air catalysts for primary Zn−air batteries, the assembled batteries deliver a large peak power density of 118 mW cm −2 and excellent operation stability. A variety of characterization results and controlled experiments demonstrate that the efficient performance of this hybrid material toward electrocatalytic reactions originates from the unique electrode configuration, intimate distribution of active species, hierarchically porous configuration, high conductivity of Ni foam, and synergistic effect of Co 3 O 4 and carbonaceous materials.

Developing high-efficiency electrocatalysts for both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is vital for the production of hydrogen on a large scale by electrocatalytic splitting of water. Herein, Fe-doped Ni(OH) nanosheets directly grown on commercial Ni foam (FeNiOH/NF) were fabricated through a facile hydrothermal method in (NH)SO aqueous solution containing iron salts. The integrated architecture with hierarchical pores is beneficial for exposing sufficient catalytically active sites and providing evaluated structural and electrical properties. In particular, the Fe-induced partial-charge-transfer greatly modifies the electronic structure of Ni(OH), which evidently promotes the electrocatalytic activity of the as-fabricated FeNiOH/NF for OER and HER. Thus, as an electrocatalyst for OER, FeNiOH/NF exhibits excellent activity with overpotentials of 271 and 318 mV to deliver current densities of 20 and 100 mA cm, respectively, with a small Tafel slope of 72 mV dec in 1.0 M KOH, demonstrating the very high level of novelty and sufficient improvement over the current state-of-the-art IrO electrocatalyst. Most importantly, there is an increase in overpotential by only 23 mV during continuous reaction for over 20 h at an applied potential of 1.62 V to deliver current density of 500 mA cm. The as-fabricated electrocatalyst also enables high HER activity with robust stability. Finally, an overall water splitting current density of 10 mA cm can be obtained at a cell voltage of 1.67 V in a two-electrode alkaline electrolyzer using FeNiOH/NF as both anode and cathode, along with impressive operation stability. This development with significant over the state-of-the-art IrO electrocatalyst can be widely extended to large-scale fabrication of versatile electrocatalysts for efficient water splitting technology.

Developing low-cost and highly efficient non-precious-metal-based bifunctional electrocatalysts for both oxygen reduction and evolution reactions concerns the key steps for the fabrication of rechargeable metal–air batteries. Herein, a rationally designed strategy is developed to join the merits of metal phosphate and carbonaceous materials for the fabrication of novel hybrid electrocatalysts. Through the self-polymerization of organophosphonic acid and cobalt salts on graphene oxide (GO) under a hydrothermal process to form cobalt phosphonate, and subsequently high-temperature pyrolysis, the N,P-codoped three-dimensional (3D) reduced-graphene-oxide-aerogel-supported (rGOA-supported) Co2P2O7 (CoPi) fine particles (CoPi/NPGA) are obtained. The pyrolysis of cobalt phosphonate introduces abundant heteroatom defects and the in situ formed CoPi particles on rGOA, wherein the rGOA permits enhanced electric conductivity and corrosion resistance. Thereby, these two aspects possess different abilities, and together endow the obtained hybrid material with enhanced electrocatalytic performance. In 0.1 M KOH, CoPi/NPGA affords a positive onset and half-wave potentials in catalyzing oxygen reduction, close to that of the Pt/C benchmark, along with impressive durability. In addition, it also exhibits considerable oxygen evolution electrochemical performance, and renders a potential of 1.57 V to achieve a current density of 10 mA cm–2 in 1.0 M KOH. Impressively, employed as the air cathode of the assembled Zn–air battery, this synthesized bifunctional catalyst enables high open-circuit potential, large powder density, and impressive cycling durability, holding great potential in practical rechargeable batteries.