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Highlights The well-conceived Pt–Ni3S2 heteronanocrystals with dual-monodispersed characteristics are synthesized through interfacial electronic modulation. The asymmetrical charge distribution at Pt–Ni3S2 hetero-interface results in the formation of high-valent Ni sites and negatively-charged Pt δ−. It eventually accelerates water dissociation and achieves the steady concurrent generation of value-added formate and hydrogen.

Abstract The non-classical anodic H2 production from 5-hydroxymethylfurfural (HMF) is very appealing for energy-saving H2 production with value-added chemical conversion due to the low working potential (~0.1 V vs RHE). However, the reaction mechanism is still not clear due to the lack of direct evidence for the critical intermediates. Herein, the detailed mechanisms are explored in-depth using in situ Raman and Infrared spectroscopy, isotope tracking, and density functional theory calculations. The HMF is observed to form two unique inter-convertible gem-diol intermediates in an alkaline medium: 5-(Dihydroxymethyl)furan-2-methanol anion (DHMFM−) and dianion (DHMFM2−). The DHMFM2− is easily oxidized to produce H2 via H− transfer, whereas the DHMFM− is readily oxidized to produce H2O via H+ transfer. The increases in potential considerably facilitate the DHMFM− oxidation rate, shifting the DHMFM− ↔ DHMFM2− equilibrium towards DHMFM− and therefore diminishing anodic H2 production until it terminates. This work captures the critical intermediate DHMFM2− leading to hydrogen production from aldehyde, unraveling a key point for designing higher performing systems.

Abstract Single‐atom catalysts (SACs) have gained substantial attention because of their exceptional catalytic properties. However, the high surface energy limits their synthesis, thus creating significant challenges for further development. In the last few years, metal–organic frameworks (MOFs) have received significant consideration as ideal candidates for synthesizing SACs due to their tailorable chemistry, tunable morphologies, high porosity, and chemical/thermal stability. From this perspective, this review thoroughly summarizes the previously reported methods and possible future approaches for constructing MOF‐based (MOF‐derived‐supported and MOF‐supported) SACs. Then, MOF‐based SAC's identification techniques are briefly assessed to understand their coordination environments, local electronic structures, spatial distributions, and catalytic/electrochemical reaction mechanisms. This review systematically highlights several photocatalytic and electrocatalytic applications of MOF‐based SACs for energy conversion and storage, including hydrogen evolution reactions, oxygen evolution reactions, O2/CO2/N2 reduction reactions, fuel cells, and rechargeable batteries. Some light is also shed on the future development of this highly exciting field by highlighting the advantages and limitations of MOF‐based SACs.

Co–N–C is a promising oxygen electrochemical catalyst due to its high stability and good durability. However, due to the limited adsorption ability improvement for oxygen-containing intermediates, it usually exhibits inadequate catalytic activity with 2-electron pathway and high selectivity of hydrogen peroxide. Herein, the adsorption of Co–N–C to these intermediates is modulated by constructing heterostructures using transition metals and their derivatives based on d-band theory. The heterostructured nanobelts with MoC core and pomegranate-like carbon shell consisting of Co nanoparticles and N dopant (MoC/Co–N–C) are engineered to successfully modulate the d band center of active Co–N–C sites, resulting in a remarkably enhanced electrocatalysis performance. The optimally performing MoC/Co–N–C exhibits outstanding bi-catalytic activity and stability for the oxygen electrochemistry, featuring a high wave-half potential of 0.865 V for the oxygen reduction reaction (ORR) and low overpotential of 370 mV for the oxygen evolution reaction (OER) at 10 mA cm−2. The zinc air batteries with the MoC/Co–N–C catalyst demonstrate a large power density of 180 mW cm−2 and a long cycling lifespan (2000 cycles). The density functional theory calculations with Hubbard correction (DFT + U) reveal the electron transferring from Co to Mo atoms that effectively modulate the d band center of the active Co sites and achieve optimum adsorption ability with “single site double adsorption” mode.

Abstract Electrocatalytic water splitting is a viable technique for generating hydrogen but is precluded from the sluggish kinetics of oxygen evolution reactions (OER). Small molecule oxidation reactions with lower working potentials, such as methanol oxidation reactions, are good alternatives to OER with faster kinetics. However, the typically employed Ni-based electrocatalysts have poor activity and stability. Herein, a novel three-dimensional (3D)-networking Mo-doped Ni(OH)2 with ultralow Ni–Ni coordination is synthesized, which exhibits a high MOR activity of 100 mA cm−2 at 1.39 V, delivering 28 mV dec−1 for the Tafel slope. Meanwhile, hydrogen evolution with value-added formate co-generation is boosted with a current density of more than 500 mA cm−2 at a cell voltage of 2.00 V for 50 h, showing excellent stability in an industrial alkaline concentration (6 M KOH). Mechanistic studies based on density functional theory and X-ray absorption spectroscopy showed that the improved performance is mainly attributed to the ultralow Ni–Ni coordination, 3D-networking structures and Mo dopants, which improve the catalytic activity, increase the active site density and strengthen the Ni(OH)2 3D-networking structures, respectively. This study paves a new way for designing electrocatalysts with enhanced activity and durability for industrial energy-saving hydrogen production.

The instability of perovskites with exsolved nanoparticles for CO2 electrocatalysis impedes their practical applications. Here, the authors show the formation of B-site vacancies in perovskite substrate as a major contributor to the degradation and report a strategy to enhance the stability of the perovskites at high voltages.

The solid oxide electrolytic cell (SOEC) is one of the most promising energy conversion and storage devices, which could convert CO2 to CO with high Faradaic efficiency and production rate. However, the lack of active and stable cathode materials impedes their practical applications. Here we focus on the promising perovskite oxide cathode material Sr2Fe1.5Mo0.5O6−σ, with the aim of understanding how A-atom stoichiometry and catalytic performance are linked. We find that increasing the strontium content in the perovskite improves the chemisorption of CO2 on its surface, forming a SrCO3 phase. This hinders the charge transfer and oxygen exchange processes. Simultaneously, strontoium segregation to the cathode surface facilitates coking of the surface during CO2 electrolysis, which poisons the electrode. Consequently, a small number of Sr deficiencies are optimal for both electrochemical performance and long-term stability. Our results provide new insights for designing high-performance CO2 electrolysis cathode materials.

Abstract Electrochemical reduction of CO2 to formate is economically attractive but improving the reaction selectivity and activity remains challenging. Herein, we introduce boron (B) atoms to modify the local electronic structure of bismuth with positive valence sites for boosting conversion of CO2 into formate with high activity and selectivity in a wide potential window. By combining experimental and computational investigations, our study indicates that B dopant differentiates the proton participations of rate-determining steps in CO2 reduction and in the competing hydrogen evolution. By comparing the experimental observations with the density functional theory, the dominant mechanistic pathway of B promoted formate generation and the B concentration modulated effects on the catalytic property of Bi are unravelled. This comprehensive study offers deep mechanistic insights into the reaction pathway at an atomic and molecular level and provides an effective strategy for the rational design of highly active and selective electrocatalysts for efficient CO2 conversion.

Abstract Efficient and robust single-atom catalysts (SACs) based on cheap and earth-abundant elements are highly desirable for electrochemical reduction of nitrogen to ammonia (NRR) under ambient conditions. Herein, for the first time, a Mn–N–C SAC consisting of isolated manganese atomic sites on ultrathin carbon nanosheets is developed via a template-free folic acid self-assembly strategy. The spontaneous molecular partial dissociation enables a facile fabrication process without being plagued by metal atom aggregation. Thanks to well-exposed atomic Mn active sites anchored on two-dimensional conductive carbon matrix, the catalyst exhibits excellent activity for NRR with high activity and selectivity, achieving a high Faradaic efficiency of 32.02% for ammonia synthesis at − 0.45 V versus reversible hydrogen electrode. Density functional theory calculations unveil the crucial role of atomic Mn sites in promoting N2 adsorption, activation and selective reduction to NH3 by the distal mechanism. This work provides a simple synthesis process for Mn–N–C SAC and a good platform for understanding the structure-activity relationship of atomic Mn sites. Graphic Abstract

The formation of light-induced oxygen vacancy (V _O ) is detected and confirmed on the surface of various metal-oxide-based semiconductors under mild reaction conditions with low cost energy source (sunlight). This self-structural transformation of the materials can bring about new characteristics and functionalities, which has inspired many researchers to explore the applications of light-induced V _O in the photochemical conversion. In this perspective, generating and maintaining the light-induced V _O are discussed based on some of the important work in the field of photochemical conversion. The effects and utilizations of the light-induced V _O are revealed including the models proposed to explain mechanism. Then, the electric current measurements and key challenges of the light-induced V _O are also summarized in a comprehensive introduction. Finally, some important aspects and questions in terms of the future research of light-induced V _O are emphasized via discussing the potential contribution and development. And the schematic of future developments for light-induced V _O is provided based on loop-locked materials design, light engineering and mechanism investigation.

Abstract The development of highly efficient electrocatalysts toward the oxygen evolution reaction is imperative for advancing water splitting technology to generate clean hydrogen energy. Herein, a two dimensional (2D) nanosheet ammonium cobalt phosphate hydrate (NH4CoPO4·H2O) catalyst based on the earth‐abundant non‐noble metal is reported. When used for the challenging alkaline saline water electrolysis, the NH4CoPO4·H2O catalyst with the optimal thickness of 30 nm achieves current densities of 10 and 100 mA cm−2 at the record low overpotentials of 252 and 268 mV, respectively, while maintaining remarkable stability during the alkaline saline water oxidation at room temperature. X‐ray absorption fine spectra reveal that the activation of Co (II) ions (in NH4CoPO4·H2O) to Co (III) species constructs the electrocatalytic active sites. The 2D nanosheet morphology of NH4CoPO4·H2O provides a larger active surface area and more surface‐exposed active sites, which enable the nanosheet catalyst to facilitate the alkaline freshwater and simulated seawater oxidation with excellent activity. The facile and environmentally‐benign H2O‐mediated synthesis route under mild condition makes NH4CoPO4·H2O catalyst highly feasible for practical manufacturing. In comparison with noble metals, this novel electrocatalyst offers a cost‐effective alternative for economic saline water oxidation to advance water electrolysis technology.

Manganese oxides (MnOx) have been regarded as promising catalyst candidates for oxygen reduction reaction (ORR) due to their natural abundance and extremely low toxicity. However, the intrinsic low conductivity of MnOx limits their application. In this work, Mn oxide embedded in N doped porous carbon (MnOx@C-N) electrocatalysts were prepared through a facile zeolitic imidazolate framework (ZIF-8) template method for ORR. The structure, morphology, and composition of the prepared materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). Electrocatalytic performances of the prepared materials were investigated by linear sweep voltammetry. Benefiting from the well-defined morphology, high surface area, and porous structure, the MnOx@C-N electrocatalyst showed the highest ORR activity among all investigated materials with the limiting current density of 5.38 mA/cm2 at a rotation speed of 1600 rpm, the positive half-wave potential of 0.645 V vs. RHE, and the electron transfer number of 3.90. This work showcases an effective strategy to enhance ORR activity of MnOx.

Abstract Electrochemical nitrate reduction (NITRR) offers a promising alternative toward nitrogen recycling and ammonia production under ambient conditions, for which highly active and selective electrocatalyst is desired. In this study, metallic cobalt nanoarrays as facilely prepared from the electrochemical reduction of Co(OH)2 nanoarrays (NAs) are demonstrated to exhibit unprecedented NH3 producing capability from catalyzing NITRR. Benefitting from the high intrinsic activity of Co0, intimate contact between active species and conductive substrate and the nanostructure which exposes large number of active sites, the Co‐NAs electrode exhibits current density of −2.2 A cm−2 and NH3 production rate of 10.4 mmol h−1 cm−2 at −0.24 V versus RHE under alkaline condition and significantly surpasses reported counterparts. Moreover, the close‐to‐unity (≥96%) Faradaic efficiency (FE) toward NH3 is achieved over wide application range (potential, NO3− concentration and pH). Density function theory calculation reveals the optimized adsorption energy of NITRR intermediates on Co surface over Co(OH)2. Furthermore, it is proposed that despite the sluggish kinetics of Volmer step (H2O → *H + *OH) which provides protons in conventional hydrogenation mechanism, the proton‐supplying water dissociation process on Co surface is drastically facilitated following a concerted water dissociation–hydrogenation pathway.

Standalone solar carbon dioxide conversion without the use of any external energy is a primary goal of solar carbon-based fuel production. So far, researchers have performed many staged studies, for example, on the independent oxygen evolution reaction and CO2 reduction reaction, to focus on these key steps and strengthen specific characteristics, including photoresponse, energy carrier separation, and transfer. Noteworthy performance has been obtained for almost every stage. However, recent pioneering works have demonstrated that staged research cannot always be easily pieced together. Here, recent advances in standalone systems are collected and reviewed. We focus on the critical assessment of the key components requiring improvement. In addition, the opportunities for hybrid systems of photocatalysts with photothermocatalysts and photovoltaics with electrocatalysts are assessed. This review aims to discuss the direction of standalone solar carbon fuel production and potential knowledge transfer to intersecting fields.

Abstract Efficient electrocatalysts for the oxygen evolution reaction (OER) are highly desirable because of the intrinsically sluggish kinetics of OER. Herein, core–shell structured nanospheres of NiFexSn@NiFe (oxy)hydroxide (denoted as NiFexSn‐A) are prepared as active OER catalysts by a facile electrochemical strategy, which includes electrodeposition of NiFexSn alloy nanospheres on carbon cloth (CC) and following anodization. The alloy core of NiFexSn could promote charge transfer, and the amorphous shell of NiFe (oxy)hydroxide is defect‐rich and nanoporous due to the selective electrochemical etching of Sn in alkaline medium. The optimized catalyst of NiFe0.5Sn‐A displays a remarkable OER performance with a low overpotential of 260 mV to reach the current density of 10 mA cm−2, a small Tafel slope of 50 mV dec−1, a high turnover frequency of 0.194 s−1 at an overpotential of 300 mV, and a robust durability. Further characterizations indicate that the superior OER performance of the core–shell structured NiFe0.5Sn‐A nanospheres might originate from abundant active sites and small charge transfer resistance. This work brings a new perspective to the design and synthesis of core–shell structured nanospheres for electrocatalysis through a facile electrochemical strategy.

Electrochemical CO2 reduction reaction (CO2RR) is a sustainable approach to producing carbon-neutral fuels when combined with renewable energies. Besides the emphatic consideration of developing efficient catalysts, a suitable conductive carbon agent served as co-catalyst with a low activity toward the competitive hydrogen evolution reaction (HER), is also highly needed. However, there have been limited studies focused on the investigation of co-catalyst during CO2RR, especially on their HER behavior. We herein explored the HER of various co-catalyst, i.e., acetylene black (AB), carbon black (CB) and graphite flake (GF) as well as carbon nanotube (CNT), and their composites with sub-25 nm Ag nanowires (NWs) as catalysts. GF and CB exhibit a higher activity toward CO2RR and HER, respectively. In contrast, CB/Ag NWs achieve the highest Faraday efficiency and partial current density for CO2RR, whereas CNT/Ag NWs prefer HER. The differences in HER suggest a critical influence of co-catalyst and this study points to a better guidance on the selection of co-catalyst for CO2RR. Keywords: Carbon dioxide reduction reaction, Hydrogen evolution reaction, Carbon support material, Ag nanowires

The unexpected scaling phenomena have resulted in significant damages to the oil and gas industries, leading to issues such as heat exchanger failures and pipeline clogging. It is of practical and fundamental importance to understand the scaling mechanisms and develop efficient anti-scaling strategies. However, the underlying surface interaction mechanisms of scalants (e.g., calcite) with various substrates are still not fully understood. In this work, the colloidal probe atomic force microscopy (AFM) technique has been applied to directly quantify the surface forces between calcite particles and different metallic substrates, including carbon steel (CR1018), low alloy steel (4140), stainless steel (SS304) and tungsten carbide, under different water chemistries (i.e., salinity and pH). Measured force profiles revealed that the attractive van der Waals (VDW) interaction contributed to the attachment of the calcium carbonate particles on substrate surfaces, while the repulsive electric double layer (EDL) interactions could inhibit the attachment behaviors. High salinity and acidic pH conditions of aqueous solutions could weaken the EDL repulsion and promote the attachment behavior. The adhesion of calcite particles with CR1018 and 4140 substrates was much stronger than that with SS304 and tungsten carbide substrates. The bulk scaling tests in aqueous solutions from an industrial oil production process showed that much more severe scaling behaviors of calcite was detected on CR1018 and 4140 than those on SS304 and tungsten carbide, which agreed with surface force measurement results. Besides, high salinity and acidic pH can significantly enhance the scaling phenomena. This work provides fundamental insights into the scaling mechanisms of calcite at the nanoscale with practical implications for the selection of suitable antiscaling materials in petroleum industries. [ABSTRACT FROM AUTHOR]