Bimetallic vanadium-molybdenum nitrides using magnetron co-sputtering as alkaline hydrogen evolution catalyst

Transition metal nitride catalysts for selective conversion of oxygen-containing molecules

Earth abundant transition metal nitrides (TMNs) are a promising group of catalysts for a wide range of thermocatalytic, electrocatalytic and photocatalytic reactions, with potential to achieve high activity and selectivity while reducing reliance on the use of Pt-group metals. However, current fundamental understanding of the active sites of these materials and the mechanisms by which selective transformations occur is somewhat lacking. Recent investigations of these materials from our group and others have utilized probe molecules, model surfaces, and in situ techniques to elucidate the origin of their activity, strong metal-support interactions, and unique d-band electronic structures. This Perspective discusses three classes of reactions for which TMNs have been used as case studies to highlight how these properties, along with synergistic interactions with metal overlayers, can be exploited to design active, selective and stable TMN catalysts. First, studies of the reactions of C1 molecules will be discussed, specifically highlighting the ability of TMNs to activate CO2. Second, the upgrading of biomass and biomass-derived oxygenates over TMN catalysts will be reviewed. Third, the use of TMNs for H2 production via water electrolysis will be discussed. Finally, we will discuss the challenges and future directions in the study of TMN catalysts, in particular expanding on opportunities to enhance fundamental mechanistic understanding using model surfaces, the elucidation of active centers via in situ techniques, and the development of efficient synthesis methods and design principles.

Hydrogen-bond induced and hetero coupling dual effects in N-doped carbon coated CrN/Ni nanosheets for efficient alkaline freshwater/seawater hydrogen evolution

Developing efficient and robust non-precious-metal-based hydrogen evolution reaction (HER) catalysts is highly desirable but remains quite challenging for alkaline freshwater/seawater electrolysis. In the present study, we report a theory-guided design and synthesis of a nickel foam (NF) supported N-doped carbon-coated (NC) nickel (Ni)/chromium nitride (CrN) nanosheets (NC@CrN/Ni) as a highly active and durable electrocatalyst. Our theoretical calculation firstly reveals that CrN/Ni heterostructure can greatly promote the H₂O dissociation via hydrogen-bond induced effect, and the N site can be optimized by hetero coupling to achieve a facile hydrogen associative desorption, thereby significantly boosting alkaline HER. Guided by theoretical calculation, we prepared the nickel-based metal-organic framework as a precursor, and introduced the Cr by the subsequent hydrothermal treatment, finally obtained the target catalyst by ammonia pyrolysis. Such a simple process ensures the exposure of abundant accessible active sites. Consequently, the as-prepared NC@CrN/Ni catalyst exhibits outstanding performance in both alkaline freshwater and seawater, with the respective overpotential of only 24 and 28 mV at a current density of 10 mA cm^-2, respectively. More impressively, the catalyst also possesses superior durability in the constant-current test of 50 h at the different current densities of 10, 100, and 1000 mA cm^-2.

Transition Metal Nitrides for Electrocatalytic Application: Progress and Rational Design

The energy crisis and environmental issues are becoming more severe due to the long-term consumption of fossil fuels. Therefore, novel energy-conversion devices with high energy density and environmental friendliness are expected to provide reliable alternatives to traditional fossil-based energy systems. However, because of the inevitable use of costly precious metals as the electrode catalysts for such devices, their popularization is seriously hindered. Transition metal nitrides (TMNs) exhibit similar surface and adsorption properties to noble metals because the atomic distance between metal atoms increases and the d-band center of metal atoms downshifts after nitrogen atoms enter the metal lattice. TMNs have become one of the best electrode materials to replace noble metal-based electrocatalysts in next-generation energy-storage and energy-conversion devices. In this review, the recent developments in the electrocatalytic application of TMNs are covered. First, we discuss the structure and activity origin of TMNs and introduce the common synthesis methods for the preparation of TMNs. Subsequently, we illustrate the applications of mono-metallic TMNs and multi-metallic TMNs in oxygen-reduction reaction, oxygen-evolution reaction, and bifunctional oxygen reduction and evolution reactions. Finally, we summarize the challenges of TMNs encountered at the present stage, and expect their future development.

Realizing Superior Redox Kinetics of Hollow Bimetallic Sulfide Nanoarchitectures by Defect-Induced Manipulation toward Flexible Solid-State Supercapacitors

As a typical battery-type material, CuCo₂ S₄ is a promising candidate for supercapacitors due to the high theoretical specific capacity. However, its practical application is plagued by inherently sluggish ion diffusion kinetics and inferior electrical transport properties. Herein, sulfur vacancies are incorporated in CuCo₂ S₄ hollow nanoarchitectures (HNs) to accelerate redox reactivity. Experimental analyses and theoretical investigations uncover that the generated sulfur vacancies increase the active electron states, reduce the adsorption barriers of electrolyte ions, and enrich reactive redox species, thus achieving enhanced electrochemical performance. Consequently, the deficient CuCo₂ S₄ with optimized vacancy concentration presents a high specific capacity of 231 mAh g^-1 at 1 A g^-1 , a ≈1.78 times increase compared to that of pristine CuCo₂ S₄ , and exhibits a superior rate capability (73.8% capacity retention at 20 A g^-1 ). Furthermore, flexible solid-state asymmetric supercapacitor devices assembled with the deficient CuCo₂ S₄ HNs and VN nanosheets deliver a high energy density of 61.4 W h kg^-1 at 750 W kg^-1 . Under different bending states, the devices display exceptional mechanical flexibility with no obvious change in CV curves at 50 mV s^-1 . These findings provide insights for regulating electrode reactivity of battery-type materials through intentional nanoarchitectonics and vacancy engineering.

Porous single-crystalline vanadium nitride octahedra with a unique electrocatalytic performance

Here we grow porous single-crystalline vanadium nitride that has a good performance in the HER, showing high activity and stability.

Metal nitride-based nanostructures for electrochemical and photocatalytic hydrogen production

The over-dependence on fossil fuels is one of the critical issues to be addressed for combating greenhouse gas emissions. Hydrogen, one of the promising alternatives to fossil fuels, is renewable, carbon-free, and non-polluting gas. The complete utilization of hydrogen in every sector ranging from small to large scale could hugely benefit in mitigating climate change. One of the key aspects of the hydrogen sector is its production via cost-effective and safe ways. Electrolysis and photocatalysis are well-known processes for hydrogen production and their efficiency relies on electrocatalysts, which are generally noble metals. The usage of noble metals as catalysts makes these processes costly and their scarcity is also a limiting factor. Metal nitrides and their porous counterparts have drawn considerable attention from researchers due to their good promise for hydrogen production. Their properties such as active metal centres, nitrogen functionalities, and porous features such as surface area, pore-volume, and tunable pore size could play an important role in electrochemical and photocatalytic hydrogen production. This review focuses on the recent developments in metal nitrides from their synthesis methods point of view. Much attention is given to the emergence of new synthesis techniques, methods, and processes of synthesizing the metal nitride nanostructures. The applications of electrochemical and photocatalytic hydrogen production are summarized. Overall, this review will provide useful information to researchers working in the field of metal nitrides and their application for hydrogen production.

Nitrogen-Doped Porous Carbon Nanosheets Strongly Coupled with Mo2C Nanoparticles for Efficient Electrocatalytic Hydrogen Evolution

Exploring earth-abundant and noble metal-free catalysts for water electrolysis is pivotal in renewable hydrogen production. Herein, a highly active electrocatalyst of nitrogen-doped porous carbon nanosheets coupled with Mo₂C nanoparticles (Mo₂C/NPC) was synthesized by a novel method with high BET surface area of 1380 m² g^-1 using KOH to activate carbon composite materials. The KOH plays a key role in etching out MoS₂ to produce Mo precursor; simultaneously, it corrodes carbon to form porous structure and produce reducing gas such as H₂ and CO. The resulting Mo₂C/NPC hybrid demonstrated superior HER activity in acid solution, with the overpotential of 166 mV at current density of 10 mA cm^-2, onset overpotential of 93 mV, Tafel slope of 68 mV dec^-1, and remarkable long-term cycling stability. The present strategy may provide a promising strategy to fabricate other metal carbide/carbon hybrids for energy conversion and storage.