Self-Supported Vanadium Carbide by an Electropolymerization-Assisted Method for Efficient Hydrogen Production

Tailoring Pseudo-Graphitic Domain by Molybdenum Modification to Boost Sodium Storage Capacity and Durability for Hard Carbon

Hard carbon (HC) stands out as the most prospective anode for sodium-ion batteries (SIBs) with significant potential for commercial applications. However, some long-standing and intractable obstacles, like low first coulombic efficiency (ICE), poor rate capability, storage capacity, and cycling stability, have severely hindered the conversion process from laboratory to commercialization. The above-mentioned issues are closely related to Na+ transfer kinetics, surface chemistry, and internal pseudo-graphitic carbon content. Herein, constructing molybdenum-modified hard carbon solid spheres (Mo2C/HC-5.0), both the ion transfer kinetics, surface chemistry, and internal pseudo-graphitic carbon content are comprehensively improved. Specifically, Mo2C/HC-5.0 with higher pseudo-graphitic carbon content provides a large number of active sites and a more stable layer structure, resulting in improved sodium storage capacity, rate performance, and cycling stability. Moreover, the lower defect density and specific surface area of Mo2C/HC-5.0 further enhance ICE and sodium storage capacity. Consequently, the Mo2C/HC-5.0 anode achieves a high capacity of 410.7 mA h g-1 and an ICE of 83.9% at 50 mA g-1. Furthermore, the material exhibits exceptional rate capability and cycling stability, maintaining a capacity of 202.8 mA h g-1 at 2 A g-1 and 214.9 mA h g-1 after 800 cycles at 1 A g-1.

Computational screening toward transition metal doped vanadium carbides in different crystal planes for efficient hydrogen evolution: a first-principles study

In the present work, we evaluated the hydrogen evolution reaction (HER) performance of transition metal (Co, Fe, Ni, Mn, and Mo) doped vanadium carbides (VC). In addition, the doping atoms were screened separately on the (100), (110) and (111) crystal planes to analyze the differences in HER activities. Among all the calculated models, Mn-VC(100) exhibited the best catalytic hydrogen evolution performance with a Gibbs free energy for hydrogen adsorption (ΔG_H*) of 0.0012 eV. Doping Mn greatly improved the HER performance of VC(100) by enhancing the adsorption of hydrogen on the catalyst surface. The analysis of the electronic density of states and charge transfer confirmed that doping transition metal atoms into the surfaces of the VC model successfully optimized the electronic structure and promoted catalytic reaction kinetics. Besides, the relationship between the catalytic activity and pH value of different models was considered, and doping Co atoms on the (100) crystal plane could effectively modify the pH value range applicable for the efficient HER. Interestingly, even if the same metal atoms were doped, various active sites of VC models exhibited different catalytic performances due to disparate exposed crystal planes and pH values. This indicates that the main exposed crystal surfaces and the pH range of application need to be considered when selecting the appropriate doping element for the catalyst.

Through-Space Electrostatic Effects of Positively Charged Substituents on the Hydrogen Evolution Reaction

Elucidating the effects of various structural components on energy-related small molecule activation is of fundamental and practical significance. Herein the inhibition effect of positively charged substituents on the hydrogen evolution reaction (HER) was reported. With the use of Cu porphyrins 1-5 containing different numbers and locations of positively charged substituents, it was demonstrated that their electrocatalytic HER activities significantly decreased when more cationic units were located close to the Cu ion: the i_cat /i_p (i_cat is the catalytic peak current, i_p is the one-electron reduction peak current) value decreased from 38 with zero cationic unit to 15 with four closely located cationic units. Inspired by this result, Cu porphyrin 6, with four meso-phenyl groups each bearing a negatively charged para-sulfonic substituent, was designed. With these anionic units, 6 outperformed the other Cu porphyrins for electrocatalytic HER under the same conditions.

Single-Step and Room-Temperature Synthesis of Laser-Induced Pt/VC Nanocomposites as Effective Bifunctional Electrocatalysts for Hydrogen Evolution and Oxygen Evolution Reactions

The development of cost-effective Pt-based electrocatalysts is of great scientific and industrial significance for improving the electrocatalytic activity of hydrogen evolution (HER) and oxygen evolution (OER) reactions for overall water splitting. In this work, unlike traditional furnace pyrolysis, we report the rapid and single-step room-temperature synthesis of Pt/VC nanocomposites with a three-dimensional (3D) network porous structure by laser irradiation technology. The resultant Pt-based composite (Pt/VC-2.84) could be applied to HER under different pH conditions. In particular, the content of Pt in Pt/VC-2.84 is only 2.84 wt %, which is far lower than that in the advanced HER electrocatalyst with the Pt content of 20 wt % (commercial 20 wt % Pt/C). In addition, Pt/VC-2.84 exhibits a boosted higher OER activity and stability than RuO2 in an alkaline medium. Most importantly, electrocatalytic results reflect that Pt/VC-2.84 reveals superior activity and stability toward overall water splitting.

Electropolymerization of Metal Clusters Establishing a Versatile Platform for Enhanced Catalysis Performance

Atomically precise metal clusters are attractive as highly efficient catalysts, but suffer from continuous efficiency deactivation in the catalytic process. Here, we report the development of an efficient strategy that enhances catalytic performance by electropolymerization (EP) of metal clusters into hybrid materials. Based on carbazole ligand protection, three polymerized metal-cluster hybrid materials, namely Poly-Cu₁₄ cba, Poly-Cu₆ Au₆ cbz and Poly-Cu₆ Ag₄ cbz, were prepared. Compared with isolated metal clusters, metal clusters immobilizing on a biscarbazole network after EP significantly improved their electron-transfer ability and long-term recyclability, resulting in higher catalytic performance. As a proof-of-concept, Poly-Cu₁₄ cba was evaluated as an electrocatalyst for reducing nitrate (NO₃ ^- ) to ammonia (NH₃ ), which exhibited ≈4-fold NH₃ yield rate and ≈2-fold Faraday efficiency enhancement compared to that of Cu₁₄ cba with good durability. Similarly, Poly-Cu₆ Au₆ cbz showed 10 times higher photocatalytic efficiency towards chemical warfare simulants degradation than the cluster counterpart.

Ir-based electrocatalysts promoted by TME-substituted polyoxovanadate-derived vanadium carbide for efficient hydrogen evolution and oxygen evolution

A novel trimethylolethane (TME)-substituted polyoxovanadate (POV) was designed as a precursor to prepare ultrasmall vanadium carbide nanoparticles, which markedly promoted the hydrogen evolution reaction and oxygen evolution reaction of iridium (Ir)-based electrocatalysts. This work is the first example employing organic ligand-substituted POV as the precursor for metal carbide, and is also the first combination of Ir and vanadium carbide, providing new insights into the design of excellent electrocatalysts.

Recent Progress in Emerging Two-Dimensional Transition Metal Carbides

As a new member in two-dimensional materials family, transition metal carbides (TMCs) have many excellent properties, such as chemical stability, in-plane anisotropy, high conductivity and flexibility, and remarkable energy conversation efficiency, which predispose them for promising applications as transparent electrode, flexible electronics, broadband photodetectors and battery electrodes. However, up to now, their device applications are in the early stage, especially because their controllable synthesis is still a great challenge. This review systematically summarized the state-of-the-art research in this rapidly developing field with particular focus on structure, property, synthesis and applicability of TMCs. Finally, the current challenges and future perspectives are outlined for the application of 2D TMCs.

Boosting the hydrogen evolution reaction activity of Ru in alkaline and neutral media by accelerating water dissociation

Electrochemical water splitting via a cathodic hydrogen evolution reaction (HER) is an advanced technology for clean H2 generation. Ru nanoparticle is a promising candidate for the state-of-the-art Pt catalyst; however, they still lack the competitiveness of Pt in alkaline and neutral media. Herein, a ternary HER electrocatalyst involving nano Ru and Cr2O3 as well as N-doped graphene (NG) that can work in alkaline and neutral media is proposed. Cr2O3 and NG feature strong binding energies for hydroxyl and hydrogen, respectively, which can accelerate the dissociation of water, whereas Ru has weak hydrogen binding energy to stimulate hydrogen coupling. The HER activity of Ru is greatly enhanced by the promoted water-dissociation effect of NG and Cr2O3. To achieve a current density of 10 mA cm-2, the as-obtained Ru-Cr2O3/NG only needs a very low overpotential of 47 mV, which outperforms the activity of Pt/C in alkaline media. The strategy proposed here, multi-site acceleration of water dissociation, provides new guidance on the design of a highly efficient, inexpensive, and biocompatible HER catalyst in nonacidic condition.

Interfacial Engineering-Triggered Bifunctionality of CoS2 /MoS2 Nanocubes/Nanosheet Arrays for High-Efficiency Overall Water Splitting

Searching for high-efficiency nonprecious bifunctional electrocatalysts for both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) is paramount for the advancement of water electrolysis technologies and the associated renewable energy devices. Modulation of electronic structure of an electrocatalyst via heterointerface engineering represents an efficient strategy to improve its electrocatalytic performance. Herein, a feasible hydrothermal synthesis of a novel heterostructured catalyst was demonstrated, comprising CoS₂ nanocubes and vertically aligned MoS₂ nanosheet arrays directly grown on flexible and conductive carbon cloth (CC) substrate (denoted as CoS₂ /MoS₂ @CC). Thanks to the elaborate interface engineering and vertically aligned nanosheet arrayed architecture, the resultant self-supported CoS₂ /MoS₂ @CC electrode possessed enriched exposed active sites, modulated electronic configuration, multidimensional mass transport channels, and outstanding mechanical strength, thereby affording exceptional electrocatalytic performances towards the HER and OER in alkaline electrolyte with overpotentials of 71 and 274 mV at 10 mA cm^-2 , respectively. In addition, a two-electrode electrolyzer assembled by CoS₂ /MoS₂ @CC required a cell voltage of 1.59 V at 10 mA cm^-2 with nearly 100 % faradaic efficiency and remarkable durability, showing great potential for scalable and economical water electrolysis.

Highly Efficient Alkaline Water Splitting with Ru-Doped Co-V Layered Double Hydroxide Nanosheets as a Bifunctional Electrocatalyst

Active electrocatalysts for the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are decisive for achieving efficient energy conversion from electricity to hydrogen fuel through water electrolysis. In this study, tremella-like Ru-doped Co-V layered double hydroxide nanosheets on Ni Foam (Ru-CoV-LDH@NF) was fabricated by a one-pot solvothermal reaction. As-prepared Ru-CoV-LDH@NF, with a nominal Ru loading of around 51.6 μg cm^-2 exhibits excellent bifunctional catalytic activity towards HER and OER in alkaline media. To accomplish a current density of 10 mA cm^-2 , it demands 32 mV and 230 mV overpotentials for HER and OER, respectively. The alkali electrolyzer utilizing Ru-CoV-LDH/NF as bifunctional electrocatalyst affords 10 mA cm^-2 electrolytic current density at an extremely low cell voltage of 1.50 V, showing excellent performance compared to a Pt/C-RuO₂ -based electrolyzer and many other bifunctional electrocatalyst-based ones. The incorporation of Ru changes the morphology of the resultant nanosheets to offer high electrochemical surface areas for electrocatalysis; at the same time, it significantly boosts the intrinsic HER/OER electrocatalytic activity. For HER, the energy barrier of the Volmer step is efficiently reduced upon Ru doping, whereas the Ru dopants optimize the absorption strength of *O intermediates to facilitate the OER process. This work offers a feasible means to optimize the Co-based hydroxide materials for improved electrocatalysis in overall water splitting.