However, the sluggish kinetics of oxygen evolution reaction (OER) in the electrolysis of water dramatically hinders its development for practical applications. [3] One of the challenges is to develop electrocatalysts with low-cost, abundance, high stability, and high catalytic activity for OER. Noble-metal oxides (such as IrO 2 and RuO 2) are most widely employed as efficient OER catalysts, but their scarcity and high cost limit their commercial application. [4] Therefore, tremendous efforts have been devoted to exploring low-cost earthabundant metals and their compounds for high-efficient and stable OER. [5] Nonprecious transition metal-based compounds, such as sulfides, [4c,6] (oxy)hydroxides, [4a,7] oxides, [4b,8] and phosphides, [4b,9] have been reported for OER owing to their tunable electronic structures and abundant active sites. Recently, 3d transition metal nitrides (TMNs) have been recognized to be promising for the OER process, which are superior to oxides, hydroxides, and sulfides, because of high electrical conductivity and enriched active sites. [10] It should be noted here that the surfaces of TMNs are easily oxidized into oxides and hydroxides. For example, the surface of catalyst was converted to metal oxyhydroxide (*OOH) owing to fast surface reconstruction and phase transition during the electrochemical The sluggish oxygen evolution reaction (OER) is a pivotal process for renewable energy technologies, such as water splitting. The discovery of efficient, durable, and earth-abundant electrocatalysts for water oxidation is highly desirable. Here, a novel trimetallic nitride compound grown on nickel foam (CoVFeN @ NF) is demonstrated, which is an ultra-highly active OER electrocatalyst that outperforms the benchmark catalyst, RuO 2 , and most of the state-of-the-art 3D transition metals and their compounds. CoVFeN @ NF exhibits ultralow OER overpotentials of 212 and 264 mV at 10 and 100 mA cm −2 in 1 m KOH, respectively, together with a small Tafel slop of 34.8 mV dec −1. Structural characterization reveals that the excellent catalytic activity mainly originates from: 1) formation of oxyhydroxide species on the surface of the catalyst due to surface reconstruction and phase transition, 2) promoted oxygen evolution possibly activated by peroxo-like (O 2 2−) species through a combined lattice-oxygen-oxidation and adsorbate escape mechanism, 3) an optimized electronic structure and local coordination environment owing to the synergistic effect of the multimetal system, and 4) greatly accelerated electron 1. Introduction Developing renewable and ecofriendly energy sources/technologies is urgently required to address environmental pollution and energy crisis. [1] Electrically driven water splitting for the production of hydrogen and oxygen has been considered as one

As one of the most important chemicals and an energy carrier, synthetic ammonia has been widely studied to meet the increasing demand. Among various strategies, electrochemical nitrogen reduction reaction (e‐NRR) is a promising way because of its green nature and easy set‐up on large‐scale. However, its practical application is extremely limited because of the very‐low production rate, which is strongly dependent on the electrocatalysts used. Therefore, searching novel efficient electrocatalysts for e‐NRR is essential to promote the technology. In this review, it highlights the insights on the mechanism for the NH3 electrochemical synthesis, recommend a reliable protocol for the ammonia detection, and systematically summarize the recent development on novel electrocatalysts, including noble metal‐based materials, single‐metal‐atom catalysts, non‐noble metal, and their compounds, and metal‐free materials, for efficient e‐NRR in both experimental and theoretical studies. Various strategies to improve the catalytic performance by increasing exposed active sites or tuning electronic structures, including surface control, defect engineering, and hybridization, are carefully discussed. Finally, perspectives and challenges are outlined. It can be expected that this review provides insightful guidance on the development of advanced catalytic systems to produce ammonia through N2 reduction.

solve the energy and environmental problems. The hydrogen production reaction from the electrolysis of water is considered to be the reverse reaction of hydrogen combustion, leading to an energy cycle with zero carbon emission. The electro catalytical water splitting is a green, environmentally friendly, and sustainable way to produce hydrogen. [2] The electrolysis of water includes the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction at the cathode. OER is a four-electron transfer process, which requires high energy to overcome the reaction energy barrier. [3] Therefore, it is of great significance to prepare high-efficiency catalysts to accelerate the OER process. Among many catalysts, noble metal oxides have been considered as the best catalysts for OER, [4] such as IrO 2 and RuO 2 . However, the high cost and low abundance hinder their practical applications on large scale. [3a] Therefore, searching for noble metal-free catalysts with high cost-to-efficiency is necessary.Non-noble transition metals and their compounds have been reported to be active and stable for water oxidation in alkaline solutions. [4] The research on inexpensive and earth-rich alternative catalysts with high activity and long-term stability has been rapidly increasing, especially for 3d-transition metals (i.e., Fe, Co, Ni, etc.)-based oxides, [5] oxyhydrates, [6] perovskites, [7] phosphides, [8] nitrides, [9] selenide, [10] and sulfides. [11] Among various non-precious transition metal-based catalysts, perovskite oxides have been particularly interesting because of their low cost, high flexibility with abundant elemental compositions, and tunable electronic structures. Some of perovskite catalysts showed comparable or even higher catalytic performance to/than the noble metal oxide catalysts, such as IrO 2 and RuO 2 . They have a general formula ABO 3 , where A is an alkaline earth metal (Ba, Sr, etc.), alkali metal (Li, Na, etc.), or rare earth metal atom (La, Pr, etc.) and B is a transition metal atom (Mn, Co, Fe, Ni, etc.) (Figure 1). In the unit cell, the A-position cation is positively charged with 12-fold oxygen coordination, while the B-position cation is positively charged with sixfold oxygen coordination. The substitution of A and/or B cations can modify the physical (e.g., electronic structure), chemical (e.g., oxidation state), and catalytic properties. In addition, a series of perovskite derivatives with different crystal structures, including double perovskites (A 2 B 2 O 6 ), [12] triple perovskites (A 3 B 3 O 9 ), [13] quadruple perovskites (A 4 B 4 O 12 ), [14] and Ruddlesden-Popper perovskites (A n+1 B n O 3n+1 (n = 1, 2, and 3)), [15] further increase the diversity Perovskite oxides are studied as electrocatalysts for oxygen evolution reactions (OER) because of their low cost, tunable structure, high stability, and good catalytic activity. However, there are two main challenges for most perovskite oxides to be efficient in OER, namely less active sites and low electrical conductivity, ...

The coexistence of ferroelectricity and magnetism in VOCl2 monolayer which is mechanically strippable from the bulk material offers a tantalizing potential for high-density multistate data storage.

Hydrogen evolution reaction (HER) is a key step for electrochemical energy conversion and storage. Developing well defined nanostructures as noble‐metal‐free electrocatalysts for HER is promising for the application of hydrogen technology. Herein, it is reported that 3D porous hierarchical CoNiP/CoxP multi‐phase heterostructure on Ni foam via an electrodeposition method followed by phosphorization exhibits ultra‐highly catalytic activity for HER. The optimized CoNiP/CoxP multi‐phase heterostructure achieves an excellent HER performance with an ultralow overpotential of 36 mV at 10 mA cm−2, superior to commercial Pt/C. Importantly, the multi‐phase heterostructure shows exceptional stability as confirmed by the long‐term potential cycles (30,000 cycles) and extended electrocatalysis (up to 500 h) in alkaline solution and natural seawater. Experimental characterizations and DFT calculations demonstrate that the strong electronic interaction at the heterointerface of CoNiP/CoP is achieved via the electron transfer from CoNiP to the heterointerface, which directly promotes the dissociation of water at heterointerface and desorption of hydrogen on CoNiP. These findings may provide deep understanding on the HER mechanism of heterostructure electrocatalysts and guidance on the design of earth‐abundant, cost‐effective electrocatalysts with superior HER activity for practical applications.

Predicted spin–valley coupling and valley polarization in two-dimensional MoSi2X4 (X = N, P, and As).

Photocatalytic CO2 conversion into reproducible chemical fuels (e.g., CO, CH3OH, or CH4) provides a promising scheme to solve the increasing environmental problems and energy demands simultaneously. However, the efficiency is severely restricted by the high overpotential of the CO2 reduction reaction (CO2RR) and rapid recombination of photoexcited carriers. Here, we propose that a novel type-II photocatalytic mechanism based on two-dimensional (2D) ferroelectric multilayers would be ideal for addressing these issues. Using density-functional theory and nonadiabatic molecular dynamics calculations, we find that the ferroelectric CuInP2S6 bilayers exhibit a staggered band structure induced by the vertical intrinsic electric fields. Different from the traditional type-II band alignment, the unique structure of the CuInP2S6 bilayer not only effectively suppresses the recombination of photogenerated electron–hole (e–h) pairs but also produces a sufficient photovoltage to drive the CO2RR. The predicted recombination time of photogenerated e–h pairs, 1.03 ns, is much longer than the transferring times of photoinduced electrons and holes, 5.45 and 0.27 ps, respectively. Moreover, the overpotential of the CO2RR will decrease by substituting an S atom with a Cu atom, making the redox reaction proceed spontaneously under solar radiation. The solar-to-fuel efficiency with an upper limit of 8.40% is achieved in the CuInP2S6 bilayer and can be further improved to 32.57% for the CuInP2S6 five-layer. Our results indicate that this novel type-II photocatalytic mechanism would be a promising way to achieve highly efficient photocatalytic CO2 conversion based on the 2D ferroelectric multilayers.

Cobalt oxyhydroxide (CoOOH) has attracted great attention in electrochemical water splitting. However, the mechanism behind its catalytic performance and how to improve its activity are still under debate. In the...