The bimetallic nickel-cobalt phosphide (NiCoP) has been confirmed as an efficient electrocatalyst in water splitting. But little attention is paid to the selectivity and affinity of metal sites on hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Herein, we report a trace-Zn-doping (2.18 wt.%) NiCoP (Zn-NiCoP) whereby the nanoparticles self-aggregated to form elongated nanoneedles. We discover that both Co and Ni sites can be replaced by Zn. The Co substitution improves HER, while the Ni substitution dramatically reduces the energy barrier of the rate-determining step (*O → *OOH). The negative shift of d-band centers after Zn doping ameliorates the intermediate desorption. Therefore, Zn-NiCoP demonstrates superior electrocatalytic activity with overpotentials of 48 and 240 mV for HER and OER at 10 and 50 mA·cm⁻², respectively. The cell voltage with Zn-NiCoP as both anode and cathode in water splitting was as low as 1.35 V at 10 mA·cm⁻².

There is an increasingly urgent need to develop cost-effective electrocatalysts with high catalytic activity and stability as alternatives to the traditional Pt/C in catalysts in water electrolysis. In this study, microspheres composed of Mo-doped NiCoP nanoneedles supported on nickel foam were prepared to address this challenge. The results show that the nanoneedles provide sufficient active sites for efficient electron transfer; the small-sized effect and the micro-scale roughness enhance the entry of reactants and the release of hydrogen bubbles; the Mo doping effectively improves the electrocatalytic performance of NiCoP in alkaline media. The catalyst exhibits low hydrogen evolution overpotentials of 38.5 and 217.5 mV at a current density of 10 mA·cm⁻² and high current density of 500 mA·cm⁻², respectively, and only 1.978 V is required to achieve a current density of 1000 mA·cm⁻² for overall water splitting. Density functional theory (DFT) calculations show that the improved hydrogen evolution performance can be explained as a result of the Mo doping, which serves to reduce the interaction between NiCoP and intermediates, optimize the Gibbs free energy of hydrogen adsorption ( $\mathrm{\Delta }{G}_{\text{*}\text{H}}$), and accelerate the desorption rate of $\text{*}\text{O}\text{H}$. This study provides a promising solution to the ongoing challenge of designing efficient electrocatalysts for high-current-density hydrogen production.

The electrochemical performance of hard carbon (HC) materials is closely related to the electrolyte used in the sodium ion batteries (SIBs). Conventional electrolytes carbonate (EC) demonstrates low initial Columbic efficiency (ICE) and poor rate performance, which is one of the main bottlenecks that limits the practical application of HCs. Ether electrolyte (diglyme) was reported to improve the rate performance of HCs. Nevertheless, the underlying mechanism for the excellent rate capability is still lack of in-depth study. In this work, the differences of sodium-ion diffusion between ether and carbonate-base electrolytes in HCs are analyzed layer by layer. Firstly, when sodium-ions are diffused in electrolyte, the diffusion coefficient of sodium-ion in ether electrolyte is about 2.5 times higher than that in ester electrolytes by molecular dynamics (MD) simulation and experimental characterization. Furthermore, when the solvated sodium-ions are diffused into the solid electrolyte interphase (SEI) interface and the HCs material, the enhanced charge transfer kinetics (thin SEI layer (4.6 vs. 12 nm) and low R_SEI (1.5 vs. 24 Ω)) at the SEI combined with low desolvation energy (0.248 eV) are responsible for high-rate performance and good cycling stability of HC in ether electrolyte. Therefore, high diffusion coefficient, low desolvation energy, and good interface are the intrinsic reasons for enhanced rate performance in ether electrolyte, which also has guiding significance for the design of other high-rate electrolytes.

In the recent times sodium ion batteries (SIBs) have come to the forefront as an economic and resourceful alternative to lithium-ion batteries (LIBs) for powering portable electronic devices and large-scale grid storage. As the specific capacity, energy density and long cycle life of batteries depend upon the performance of anode materials; their quest is the ultimate need of the hour. Among the anode materials, the semimetallic pnictogens (As, Sb, Bi) and their compounds offer high gravimetric/volumetric capacities, but suffer from undesired volume expansion and inferior electrical conductivity. Herein, this paper reviews the recent progress in semimetallic pnictogens as alloying anodes and their compounds mainly as conversion-alloying anodes. Various debatable sodiation mechanisms (intercalation or alloying) have been presented with emphasis on in situ/ex situ advanced characterization methods well supported by theoretical modeling and calculations. The reviewed electrochemical reaction mechanisms, coherent structural designs and engineering provide a vital understanding of the electrochemical processes of Na⁺ ion storage. The existing challenges and perspectives are also presented, and several research directions are proposed from the aspects of special morphological design, employing conductive substrates, electrolyte additives and reducing particle size for technical and commercial success of SIBs.