Defect engineering associated with cationic vacancies for promoting electrocatalytic water splitting in iron-doped Ni2P nanosheet arrays

Tuning the Electronic Structure of Ni2P through Fe Doping to Trigger the Lattice-Oxygen-Mediated Oxygen Evolution Reaction

Developing cost-effective electrocatalysts for efficient seawater splitting requires a fundamental understanding of the oxygen evolution reaction (OER) mechanism. Herein, iron-doped nickel phosphide (Fe-Ni2P) is synthesized via a hydrothermal-impregnation-phosphidation strategy to investigate the role of Fe incorporation in modulating the electronic structure and OER pathways. Mechanistic investigations demonstrate that Fe doping triggers a shift from adsorbate evolution mechanism (AEM) to lattice oxygen-mediated (LOM) pathways, evidenced by pH-dependent kinetics, tetramethylammonium cation probing, and in situ electrochemical impedance spectroscopy (EIS). The LOM mechanism involves nonconcerted proton-electron transfers, facilitated by accelerated hydroxide adsorption (ks = 0.275 s-1) and dynamic surface reconstruction into amorphous NiOOH. The reduced activation energy (27.1 kJ mol-1) and lower charge-transfer resistance in Fe-Ni2P underscore its superior thermodynamics and kinetics. X-ray photoelectron spectroscopy and EIS further validate lattice oxygen activation and oxygen vacancy accumulation during the OER process. Electrochemical studies reveal that Fe-Ni2P exhibits a low overpotential of 220 mV at 10 mA cm-2 and remarkable stability through phosphate-mediated Cl- repulsion and dynamic surface reconstruction involving lattice oxygen activation in alkaline seawater. This work establishes Fe-induced electronic modulation as a critical strategy for activating LOM-dominated catalysis in transition metal phosphides.

A synergistic coordination-reduction interface for electrochemical reductive extraction of uranium with low impurities from seawater

Electrochemical extraction of uranium from seawater is a promising strategy for the sustainable supply of nuclear fuel, whereas the current progress suffers from the co-deposition of impurities. Herein, we construct a synergistic coordination-reduction interface in CMOS@NSF, achieving electrochemical extraction of black UO2 product from seawater. The internal sulfur of CoMoOS tailors the electron distribution, resulting in the electron accumulation of terminal O sites for strong uranyl binding. Meanwhile, the interfacial connection of CoMoOS with Ni3S2 accelerates the electron transfer and promoted the reductive properties. Such synergistic coordination-reduction interface ensures the formation and preservation of tetravalent uranium, preventing the co-deposition of alkalis in crystalline transformation. From natural seawater, CMOS@NSF exhibits an electrochemical extraction capacity of 2.65 mg g-1 d-1 with black UO2 solid products as final products. This work provides an efficient strategy for the electrochemical uranium extraction from seawater with low impurities.

A new insight into vacancy modulation in lead-doped tungsten oxide nonarchitect for photoelectrochemical water splitting: An experimental and density functional theory approach

In this study, the impact of lead (Pb) doping on the photoelectrochemical (PEC) water splitting performance of tungsten oxide (WO3) photoanodes was investigated through a combination of experimental and theoretical approaches. Pb-doped WO3 nanostructured thin films were synthesized hydrothermally, and extensive characterizations were conducted to study their morphologies, band edge, optical and photoelectrochemical properties. Pb-doped WO3 exhibited efficient carrier density and charge separations by reducing the charge transfer resistance. The 0.96 at% Pb doping shows a record photocurrent of ∼ 1.49 mAcm-2 and ∼ 3.44 mAcm-2 (with the hole scavenger) at 1.23 V vs. RHE besides yielding a high charge separation and Faradaic efficiencies of ∼ 86 % and > 90 %, respectively. A shift in the Fermi level towards the conduction band was also observed upon the Pb doping. Additionally, density functional theory (DFT) simulations demonstrated the changes in the density of states and bandgap upon Pb doping, exhibiting favorable changes in the surface and bulk properties of WO3.

The progress of research on vacancies in HMF electrooxidation

5-Hydroxymethylfurfural (HMF), serving as a versatile platform compound bridging biomass resource and the fine chemicals industry, holds significant importance in biomass conversion processes. The electrooxidation of HMF plays a crucial role in yielding the valuable product (2,5-furandicarboxylic acid), which finds important applications in antimicrobial agents, pharmaceutical intermediates, polyester synthesis, and so on. Defect engineering stands as one of the most effective strategies for precisely synthesizing electrocatalytic materials, which could tune the electronic structure and coordination environment, and further altering the adsorption energy of HMF intermediate species, consequently increasing the kinetics of HMF electrooxidation. Thereinto, the most routine and effective defect are the anionic vacancies and cationic vacancies. In this concise review, the catalytic reaction mechanism for selective HMF oxidation is first elucidated, with a focus on the synthesis strategies involving both anionic and cationic vacancies. Recent advancements in various catalytic oxidation systems for HMF are summarized and synthesized from this perspective. Finally, the future research prospects for selective HMF oxidation are discussed.

Design and multilevel regulation of transition metal phosphides for efficient and industrial water electrolysis

Renewable energy electrolysis of water to produce hydrogen is an effective measure to break the energy dilemma. However, achieving activity and stability at a high current density is still a key problem in water electrolyzers. Transition metal phosphides (TMPs), with high activity and relative inexpensiveness, have become excellent candidates for the production of highly pure green hydrogen for industrial applications. In this mini-review, multilevel regulation strategies including nanoscale control, surface composition and interface structure design of high-performance TMPs for hydrogen evolution are systematically summarized. On this basis, in order to achieve large-scale hydrogen production in industry, the hydrogen evolution performance and stability of TMPs at a high current density are also discussed. Peculiarly, the practical application and requirements in proton exchange membrane (PEM) or anion exchange membrane (AEM) electrolyzers can guide the advanced design of regulatory strategies of TMPs for green hydrogen production from renewable energy. Finally, the challenges and prospects in the future development trend of TMPs for efficient and industrial water electrolysis are given.