Heterostructure of polyoxometalate/zinc-iron-oxide nanoplates as an outstanding bifunctional electrocatalyst for the hydrogen and oxygen evolution reaction

Two-dimensional correlation infrared spectroscopy study on vanadoborate anionic skeleton regulated by countercations

Two novel vanadoborate compounds, [Cu(en)2]3[Li(H2O)]4[Li(H2O)3]2[V12B18O50(OH)10(H2O)]2·33.5H2O (1) and (H2en)4[Li(H2O)]4[V12B18O55(OH)5(H2O)]·14H2O (2), were synthesized via hydrothermal synthesis under identical conditions except for temperature. Structural analysis revealed that although both contain [V12B18O60]n- cluster anion, the different countercations potentially lead to variations in the [V12B18O60]n- cluster anion skeletons. In compound 1, the V4+/V5+ ratio was 10:2; while in compound 2 the ratio was 11:1. It is speculated that different countercations may influence the valence states of cluster anions. In this study, quantum chemical calculations revealed that the aromaticity and activity of the two compounds were different, and two-dimensional correlation infrared spectroscopy (2D-COS-IR) under magnetic perturbation confirmed that distinct response peaks of functional group vibrations to the magnetic field due to the different V4+/V5+ ratios and aromaticity of the two compounds. An electrochemical analysis revealed that compound 2 exhibits higher electrocatalytic activity. The results of quantum chemical calculations are aligned not only with the changes in the 2D-COS-IR spectra but also with the conclusions obtained from experiments on electrochemical properties. Overall, this work proposes a novel strategy for interpreting the alteration of vanadoborate anionic skeleton due to the introduction of different countercations by combining 2D-COS-IR with quantum chemical calculations.

Polyoxometalate-Structured Materials: Molecular Fundamentals and Electrocatalytic Roles in Energy Conversion

Polyoxometalates (POMs), a kind of molecular metal oxide cluster with unique physical-chemical properties, have made essential contributions to creating efficient and robust electrocatalysts in renewable energy systems. Due to the fundamental advantages of POMs, such as the diversity of molecular structures and large numbers of redox active sites, numerous efforts have been devoted to extending their application areas. Up to now, various strategies of assembling POM molecules into superstructures, supporting POMs on heterogeneous substrates, and POMs-derived metal compounds have been developed for synthesizing electrocatalysts. From a multidisciplinary perspective, the latest advances in creating POM-structured materials with a unique focus on their molecular fundamentals, electrocatalytic roles, and the recent breakthroughs of POMs and POM-derived electrocatalysts, are systematically summarized. Notably, this paper focuses on exposing the current states, essences, and mechanisms of how POM-structured materials influence their electrocatalytic activities and discloses the critical requirements for future developments. The future challenges, objectives, comparisons, and perspectives for creating POM-structured materials are also systematically discussed. It is anticipated that this review will offer a substantial impact on stimulating interdisciplinary efforts for the prosperities and widespread utilizations of POM-structured materials in electrocatalysis.

Enhancing the electrochemical activity of zinc cobalt sulfide via heterojunction with MoS2 metal phase for overall water splitting

The integration of diverse components into a single heterostructure represents an innovative approach that boosts the quantity and variety of active centers, thereby enhancing the catalytic activity for both hydrogen evolution reactions (HER) and oxygen evolution reactions (OER) in the water splitting process. In this study, a novel, hierarchically porous one-dimensional nanowire array comprising zinc cobalt sulfide and molybdenum disulfide (MoS2@Zn0.76Co0.24S) was successfully synthesized on a Ni foam substrate using an efficient and straightforward hydrothermal synthesis strategy. The incorporation of the metallic phase of molybdenum disulfide elevates the electronic conductivity of MoS2@Zn0.76Co0.24S, resulting in impressively low overpotentials. At 20, 50, and 100 mA cm-2, the overpotentials for oxygen evolution reaction (OER) are merely 90 mV, 170 mV, and 240 mV, respectively. Similarly, for hydrogen evolution reaction (HER), the overpotentials are 169 mV, 237 mV, and 301 mV at the same current densities in 1.0 M potassium hydroxide solution. The utilization of the MoS2@Zn0.76Co0.24S /NF electrolyzer demonstrates its exceptional performance as a catalyst in alkaline electrolyzers. Operating at a mere 1.45 V and 10 mA cm-2, it showcases outstanding efficiency. Achieving a current density of 405 mA cm-2, the system generates hydrogen at a rate of 3.1 mL/min with a purity of 99.997%, achieving an impressive cell efficiency of 68.28% and a voltage of 1.85 V. Furthermore, the MoS2@Zn0.76Co0.24S /NF hybrid exhibits seamless integration with solar cells, establishing a photovoltaic electrochemical system for comprehensive water splitting. This wireless assembly harnesses the excellent performance of the hybrid nanowire, offering a promising solution for efficient, durable, and cost-effective bifunctional electrocatalysts in the realm of renewable energy.

Polyoxometalates@Metal-Organic Frameworks Derived Bimetallic Co/Mo2 C Nanoparticles Embedded in Carbon Nanotube-Interwoven Hierarchically Porous Carbon Polyhedron Composite as a High-Efficiency Electrocatalyst for Al-S Batteries

Al-S battery (ASB) is a promising energy storage device, notable for its safety, crustal abundance, and high theoretical energy density. However, its development faces challenges due to slow reaction kinetics and poor reversibility. The creation of a multifunctional cathode material that can both adsorb polysulfides and accelerate their conversion is key to advancing ASB. Herein, a composite composed of polyoxometalate nanohybridization-derived Mo2 C and N-doped carbon nanotube-interwoven polyhedrons (Co/Mo2 C@NCNHP) is proposed for the first time as an electrochemical catalyst in the sulfur cathode. This composite improves the utilization and conductivity of sulfur within the cathode. DFT calculations and experimental results indicate that Co enables the chemisorption of polysulfides while Mo2 C catalyzes the reduction reaction of long-chain polysulfides. X-ray photoelectron spectroscopy (XPS) and in situ UV analysis reveal the different intermediates of Al polysulfide species in Co/Mo2 C@NCNHP during discharging/charging. As a cathode material for ASB, Co/Mo2 C@NCNHP@S composite can deliver a discharge-charge voltage hysteresis of 0.75 V with a specific capacity of 370 mAh g-1 after 200 cycles at 1A g-1 .

Electronic redistribution over the active sites of NiWO4-NiO induces collegial enhancement in hydrogen evolution reaction in alkaline medium

The activity-enhancement of a new-generation catalyst focuses on the collegial approach among specific solids which exploit the mutual coactions of these materials for HER applications. Strategic manipulation of these solid interfaces typically reveals unique electronic states different from their pure phases, thus, providing a potential passage to create catalysts with excellent activity and stability. Herein, the formation of the NiWO₄-NiO interface has been designed and synthesized via a three-step method. This strategy enhances the chance of the formation of abundant heterointerfaces due to the fine distribution of NiWO₄ nanoparticles over Ni(OH)₂ sheets. NiWO₄-NiO has superior HER activity in an alkaline (1 M KOH) electrolyte with modest overpotentials of 68 mV at 10 mA cm^-2 current density. The catalyst is highly stable in an alkaline medium and negligible change was observed in the current density even after 100 h of continuous operation. This study explores a unique method for high-performance hydrogen generation by constructing transition metal-oxides heterojunction. The XPS studies reveal an electronic redistribution driven by charge transfer through the NiWO₄-NiO interface. The density functional theory (DFT) calculations show that the NiWO₄-NiO exhibits a Pt-like activity with the hydrogen Gibbs free energy (ΔG_H*) value of 0.06 eV compared to the Pt(ΔG_H* = -0.02 eV).