Defect engineering tuning electron structure of biphasic tungsten-based chalcogenide heterostructure improves its catalytic activity for hydrogen evolution and triiodide reduction

Vacancy Engineering in 2D Transition Metal Chalcogenide Photocatalyst: Structure Modulation, Function and Synergy Application

Transition metal chalcogenides (TMCs) are widely used in photocatalytic fields such as hydrogen evolution, nitrogen fixation, and pollutant degradation due to their suitable bandgaps, tunable electronic and optical properties, and strong reducing ability. The unique 2D malleability structure provides a pre-designed platform for customizable structures. The introduction of vacancy engineering makes up for the shortcomings of photocorrosion and limited light response and provides the greatest support for TMCs in terms of kinetics and thermodynamics in photocatalysis. This work reviews the effect of vacancy engineering on photocatalytic performance based on 2D semiconductor TMCs. The characteristics of vacancy introduction strategies are summarized, and the development of photocatalysis of vacancy engineering TMCs materials in energy conversion, degradation, and biological applications is reviewed. The contribution of vacancies in the optical range and charge transfer kinetics is also discussed from the perspective of structure manipulation. Vacancy engineering not only controls and optimizes the structure of the TMCs, but also improves the optical properties, charge transfer, and surface properties. The synergies between TMCs vacancy engineering and atomic doping, other vacancies, and heterojunction composite techniques are discussed in detail, followed by a summary of current trends and potential for expansion.

Te-doped-WSe2/W as a stable monolith catalyst for ampere-level current density hydrogen evolution reaction

The development of efficient electrocatalysts for the hydrogen evolution reaction (HER) holds immense importance in the context of large-scale hydrogen production from water. Nevertheless, the practical application of such catalysts still relies on precious platinum-based materials. There is a pressing need to design high-performing, non-precious metal electrocatalysts capable of generating hydrogen at substantial current levels. We report here a stable monolith catalyst of Te-doped-WSe2 directly supported by a highly conductive W mesh. This catalyst demonstrates outstanding electrocatalytic performance and stability in acidic electrolytes, especially under high current conditions, surpassing the capabilities of commercial 5% Pt/C catalysts. Specifically, at current densities of 10 and 1200 mA cm-2, it exhibits a minimal overpotential of 79 and 232 mV, along with a small Tafel slope of 55 mV dec-1, respectively. The remarkable catalytic activity of Te-WSe2 can be attributed to the exceptional electron transfer facilitated by the stable monolithic structure, as well as the abundant and efficient active sites in the material. In addition, density functional theory calculations further indicate that Te doping adjusts H atom adsorption on various positions of WSe2, making it closer to thermal neutrality compared to the original material. This study presents an innovative approach to develop cost-effective HER electrocatalysts that perform optimally under high current density conditions.

Colloid synthesis of Ni12P5/N, S-doped graphene as efficient bifunctional catalyst for alkaline hydrogen evolution and triiodide reduction reaction

Designing high-efficient bifunction catalysts with excellent catalytic activity and enhanced charge-transfer capability in both alkaline hydrogen evolution reaction (HER) and triiodide reduction reaction (IRR) is of utmost significance to advance the development of green hydrogen production and photovoltaics, respectively, yet remains a crucial challenge. Here, highly dispersed and small-sized Ni12P5 nanocrystals with narrow size distribution was well attached on the surface of N, S co-doped graphene (Ni12P5/NSG) by the facile hot-injection method. As expected, the optimized Ni12P5/NSG requires a relatively low overpotential of 132.94 ± 0.08 mV to deliver a current density of 10 mA cm-2 in alkaline condition, accompanied with remarkable long-time durability with negligible attenuation over 50 h. Density functional theory (DFT) calculations revealed that the positively synergic effect between Ni12P5 and NSG are in favor of modulating the rate determining step of the dissociation of H2O to *(OH-H), thereby upgrading its HER activity. When used as the counter electrode catalyst for IRR in DSSCs, the resultant Ni12P5/NSG exhibits extraordinary Pt-like catalytic activity and well electrochemical stability in iodide-based electrolyte, delivering a high photoelectric conversion performance (PCE) comparable to Pt. The improved PCE can be attributed to the accelerated interfacial charge-transfer capability around active sites for facilitating the reaction kinetics of IRR, as demonstrated by DFT calculations. This work provides an effective strategy for synthesizing cost-effective composites with multi-active sites and offering valuable insight into the structure-performance relationship, which is conducive to guide the synthesis of promising catalysts in the energy conversion field.

Niobium- and cobalt-modified dual-source-derived porous carbon with a honeycomb-like stable structure for supercapacitor and hydrogen evolution reaction

Designing porous carbon materials with tailored architecture and appropriate compositions is essential for supercapacitor (SC) and hydrogen evolution reaction (HER). Herein, Nb/Co-modified dual-source porous carbon (Nb/Co-DSPC) with a honeycomb structure was obtained by introducing a secondary carbon source (Co/Zn-ZIF) and transition metal Nb into activated Typha carbon (ATC). The addition of a secondary carbon source and Nb resulted in superior specific surface area (1272.38 m²/g), excellent hydrophilicity (34.73°) and abundant bimetallic active sites (Nb/Co-N_x) in Nb/Co-DSPC, providing excellent charge storage capacity and electrocatalytic activity. The Nb/Co-DSPC electrode displayed an outstanding capacitance of 337 F/g at 0.5 A/g and showed excellent stability after 15,000 charge-discharge cycles. In addition, Nb/Co-DSPC shows an overpotential of 114 mV at 10 mA cm^-2, better than those of Co-DSPC (139 mV) and ATC (162 mV) alone. This study offers a reliable strategy for advanced multifunctional porous carbon electrode materials preparations.

Constructing Molybdenum Phosphide@Cobalt Phosphide Heterostructure Nanoarrays on Nickel Foam as a Bifunctional Electrocatalyst for Enhanced Overall Water Splitting

The construction of multi-level heterostructure materials is an effective way to further the catalytic activity of catalysts. Here, we assembled self-supporting MoS₂@Co precursor nanoarrays on the support of nickel foam by coupling the hydrothermal method and electrostatic adsorption method, followed by a low-temperature phosphating strategy to obtain Mo₄P₃@CoP/NF electrode materials. The construction of the Mo₄P₃@CoP heterojunction can lead to electron transfer from the Mo₄P₃ phase to the CoP phase at the phase interface region, thereby optimizing the charge structure of the active sites. Not only that, the introduction of Mo₄P₃ will make water molecules preferentially adsorb on its surface, which will help to reduce the water molecule decomposition energy barrier of the Mo₄P₃@CoP heterojunction. Subsequently, H* overflowed to the surface of CoP to generate H₂ molecules, which finally showed a lower water molecule decomposition energy barrier and better intermediate adsorption energy. Based on this, the material shows excellent HER/OER dual-functional catalytic performance under alkaline conditions. It only needs 72 mV and 238 mV to reach 10 mA/cm² for HER and OER, respectively. Meanwhile, in a two-electrode system, only 1.54 V is needed to reach 10 mA/cm², which is even better than the commercial RuO₂/NF||Pt/C/NF electrode pair. In addition, the unique self-supporting structure design ensures unimpeded electron transmission between the loaded nanoarray and the conductive substrate. The loose porous surface design is not only conducive to the full exposure of more catalytic sites on the surface but also facilitates the smooth escape of gas after production so as to improve the utilization rate of active sites. This work has important guiding significance for the design and development of high-performance bifunctional electrolytic water catalysts.

Understanding systematic growth mechanism of porous Zn1-xCdxSe/TiO2 nanorod heterojunction from ZnSe(en)0.5/TiO2 photoanodes for bias-free solar hydrogen evolution

Herein, a porous Zn_1-xCd_xSe structure was developed on TiO₂ nanorod (NR) array for photoelectrochemical (PEC) application. Firstly, TiO₂ NR and ZnO/TiO₂ NR photoanode were synthesized via a series of hydrothermal methods on FTO. Next, the solvothermal synthesis method was adopted to develop inorganic-organic hybrid ZnSe(en)_0.5 on ZnO /TiO₂ NR-based electrode using different concentrations of the selenium (Se). We found that the ZnO NR acts as a mother material for the formation of inorganic-organic hybrid ZnSe(en)_0.5, whereas TiO₂ NR acts as a building block. In order to further improve the PEC charge transfer performance, inorganic-organic hybrid ZnSe(en)_0.5/TiO₂ NR electrode was transferred into a porous Zn_1-xCd_xSe/TiO₂ NR photoanode using the Cd²⁺ ion-exchange method. The optimized porous Zn_1-xCd_xSe/TiO₂ NR -(2) photoanode converted from ZnSe(en)_0.5 -(2) electrode (optimized Se concentration) showed a higher photocurrent density of 6.6 mA·cm^-2 at applied potential 0 V vs. Ag/AgCl. The enhanced photocurrent density was owing to the effective light absorption, enhanced charge separation, delay the charge recombination, and porous structure of Zn_1-xCd_xSe. This work highlights the promising strategy for the synthesis of porous Zn_1-xCd_xSe/TiO₂ NR from inorganic-organic ZnSe(en)_0.5/TiO₂ NR for effective charge separation and prolonging the lifetime during the photoelectrochemical reaction.

Engineering Coupled NiSx -WO2.9 Heterostructure as pH-Universal Electrocatalyst for Hydrogen Evolution Reaction

Exploiting highly active and low-cost materials as pH-universal electrocatalysts for the hydrogen evolution reaction (HER) and achieving high-purity hydrogen fuel is highly desirable but remains challenging. Herein, a novel type of coupled heterostructure was designed by simple electrodeposition followed by a sulfurization treatment. This hierarchical structure was composed of nickel sulfides (NiS, NiS₂ , denoted as NiS_x ) and oxygen-deficient tungsten oxide (WO_2.9 ), which was directly grown on nickel foam (NF) as self-supporting electrodes (NiS_x -WO_2.9 /NF) for HER over a wide pH range. The systematic experimental characterizations confirmed that the material had abundant catalytic active sites, fast interfacial electron transfer ability, and strong electronic interaction, resulting in the optimized reaction kinetics for HER. Consequently, the NiS_x -WO_2.9 /NF catalyst required low overpotentials of 96 and 117 mV to reach current densities of 50 and 100 mA cm^-2 in an alkaline medium, outperforming most of the reported non-noble metal-based materials. Moreover, this self-supported electrode exhibited impressive performance over a wide pH range, only requiring 220 and 304 mV overpotential at 100 mA cm^-2 in 0.5 m H₂ SO₄ and 1 m phosphate-buffered saline electrolytes. This work may offer a new approach to the development of advanced pH-universal electrodes for hydrogen production.

Designing a Built-In Electric Field for Efficient Energy Electrocatalysis

To utilize intermittent renewable energy as well as achieve the goals of peak carbon dioxide emissions and carbon neutrality, various electrocatalytic devices have been developed. However, the electrocatalytic reactions, e.g., hydrogen evolution reaction/oxygen evolution reaction in overall water splitting, polysulfide conversion in lithium-sulfur batteries, formation/decomposition of lithium peroxide in lithium-oxygen batteries, and nitrate reduction reaction to degrade sewage, suffer from sluggish kinetics caused by multielectron transfer processes. Owing to the merits of accelerated charge transport, optimized adsorption/desorption of intermediates, raised conductivity, regulation of the reaction microenvironment, as well as ease to combine with geometric characteristics, the built-in electric field (BIEF) is expected to overcome the above problems. Here, we give a Review about the very recent progress of BIEF for efficient energy electrocatalysis. First, the construction strategies and the characterization methods (qualitative and quantitative analysis) of BIEF are summarized. Then, the up-to-date overviews of BIEF engineering in electrocatalysis, with attention on the electron structure optimization and reaction microenvironment modulation, are analyzed and discussed in detail. In the end, the challenges and perspectives of BIEF engineering are proposed. This Review gives a deep understanding on the design of electrocatalysts with BIEF for next-generation energy storage and electrocatalytic devices.