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Ru nanoparticles have been demonstrated to be highly active electrocatalysts for the hydrogen evolution reaction (HER). At present, most of Ru nanoparticles-based HER electrocatalysts with high activity are supported by heteroatom-doped carbon substrates. Few metal oxides with large band gap (more than 5 eV) as the substrates of Ru nanoparticles are employed for the HER. By using large band gap metal oxides substrates, we can distinguish the contribution of Ru nanoparticles from the substrates. Here, a highly efficient Ru/HfO2 composite is developed by tuning numbers of Ru-O-Hf bonds and oxygen vacancies, resulting in a 20-fold enhancement in mass activity over commercial Pt/C in an alkaline medium. Density functional theory (DFT) calculations reveal that strong metal-support interaction via Ru-O-Hf bonds and the oxygen vacancies in the supported Ru samples synergistically lower the energy barrier for water dissociation to improve catalytic activities.

Regulating competitive reaction pathways to direct the selectivity of electrochemical CO2 reduction reaction toward a desired product is crucial but remains challenging. Herein, switching product from HCOOH to CO is achieved by incorporating Sb element into the CuS, in which the Cu−S ionic bond is coupled with S−Sb covalent bond through bridging S atoms that elongates the Cu−S bond from 2.24 Å to 2.30 Å. Consequently, CuS with a shorter Cu−S bond exhibited a high selectivity for producing HCOOH, with a maximum Faradaic efficiency (FE) of 72 %. Conversely, Cu3SbS4 characterized by an elongated Cu−S bond exhibited the most pronounced production of CO with a maximum FE of 60 %. In situ spectroscopy combined with density functional theory calculations revealed that the altered Cu−S bond length and local coordination environment make the *HCOO binding energy weaker on Cu3SbS4 compared to that on CuS. Notably, a volcano‐shaped correlation between the Cu−S bond length and adsorption strength of *COOH indicates that Cu−S in Cu3SbS4 as double‐active sites facilitates the adsorption of *COOH, and thus results in the high selectivity of Cu3SbS4 toward CO. [ABSTRACT FROM AUTHOR]

Lithium-excess 3d-transition-metal layered oxides (Li1+xNiyCozMn1-x-y-zO2, >250 mAh g-1) suffer from severe voltage decay upon cycling, which decreases energy density and hinders further research and development. Nevertheless, the lack of understanding on chemical and structural uniqueness of the material prevents the interpretation of internal degradation chemistry. Here, we discover a fundamental reason of the voltage decay phenomenon by comparing ordered and cation-disordered materials with a combination of X-ray absorption spectroscopy and transmission electron microscopy studies. The cation arrangement determines the transition metal-oxygen covalency and structural reversibility related to voltage decay. The identification of structural arrangement with de-lithiated oxygen-centred octahedron and interactions between octahedrons affecting the oxygen stability and transition metal mobility of layered oxide provides the insight into the degradation chemistry of cathode materials and a way to develop high-energy density electrodes.

Aluminum-air batteries are promising candidates for next-generation high-energy-density storage, but the inherent limitations hinder their practical use. Here, we show that silver nanoparticle-mediated silver manganate nanoplates are a highly active and chemically stable catalyst for oxygen reduction in alkaline media. By means of atomic-resolved transmission electron microscopy, we find that the formation of stripe patterns on the surface of a silver manganate nanoplate originates from the zigzag atomic arrangement of silver and manganese, creating a high concentration of dislocations in the crystal lattice. This structure can provide high electrical conductivity with low electrode resistance and abundant active sites for ion adsorption. The catalyst exhibits outstanding performance in a flow-based aluminum-air battery, demonstrating high gravimetric and volumetric energy densities of ~2552 Wh kgAl-1 and ~6890 Wh lAl-1 at 100 mA cm-2, as well as high stability during a mechanical recharging process.

Small coin cell batteries are predominantly used for testing lithium‐ion batteries (LIBs) in academia because they require small amounts of material and are easy to assemble. However, insufficient attention is given to difference in cell performance that arises from the differences in format between coin cells used by academic researchers and pouch or cylindrical cells which are used in industry. In this article, we compare coin cells and pouch cells of different size with exactly the same electrode materials, electrolyte, and electrochemical conditions. We show the battery impedance changes substantially depending on the cell format using techniques including Electrochemical Impedance Spectroscopy (EIS) and Galvanostatic Intermittent Titration Technique (GITT). Using full cell NCA‐graphite LIBs, we demonstrate that this difference in impedance has important knock‐on effects on the battery rate performance due to ohmic polarization and the battery life time due to Li metal plating on the anode. We hope this work will help researchers getting a better idea of how small coin cell formats impact the cell performance and help predicting improvements that can be achieved by implementing larger cell formats. [ABSTRACT FROM AUTHOR]

Although great efforts on the delicate construction of a built‐in electric field (BIEF) to modify the electronic properties of active sites have been conducted, the substantial impact of BIEF coupled with electrode potential on the electrochemical reactions has not been clearly investigated. Herein, we designed an alkaline hydrogen evolution reaction (HER) catalyst composed of heterogeneous Ru−CoP urchin arrays on carbon cloth (Ru−CoP/CC) with a strong BIEF with the guidance of density functional theory (DFT) calculations. Impressively, despite its unsatisfactory activity at 10 mA cm−2 (overpotential of 44 mV), Ru−CoP/CC exhibited better activity (357 mV) than the benchmark Pt/C catalyst (505 mV) at 1 A cm−2. Experimental and theoretical studies revealed that strong hydrogen adsorption on the interfacial Ru atoms created a high energy barrier for hydrogen desorption and spillover, resulting in unsatisfactory activity at low current densities. However, as the electrode potential became more negative (i.e. the current density increased), the barrier for hydrogen spillover from the interfacial Ru to the Co site, which had near‐zero hydrogen adsorption energy, significantly decreased, thus greatly accelerating the whole alkaline HER process. This explains why the activity of Ru−CoP is relatively susceptible to the electrode potential compared to Pt/C. [ABSTRACT FROM AUTHOR]

Even though grain boundaries (GBs) have been previously employed to increase the number of active catalytic sites or tune the binding energies of reaction intermediates for promoting electrocatalytic reactions, the effect of GBs on the tailoring of the local chemical environment on the catalyst surface has not been clarified thus far. In this study, a GBs‐enriched iridium (GB−Ir) was synthesized and examined for the alkaline hydrogen evolution reaction (HER). Operando Raman spectroscopy and density functional theory (DFT) calculations revealed that a local acid‐like environment with H3O+ intermediates was created in the GBs region owing to the electron‐enriched surface Ir atoms at the GBs. The H3O+ intermediates lowered the energy barrier for water dissociation and provided enough hydrogen proton to promote the generation of hydrogen spillover from the sites at the GBs to the sites away from the GBs, thus synergistically enhancing the hydrogen evolution activity. Notably, the GB−Ir catalyst exhibited a high alkaline HER activity (10 mV @ 10 mA cm−2, 20 mV dec−1). We believe that our findings will promote further research on GBs and the surface science of electrochemical reactions. [ABSTRACT FROM AUTHOR]

Lithium (Li) metal batteries (LMBs) are the "holy grail" in the energy storage field due to their high energy density (theoretically >500 Wh kg−1). Recently, tremendous efforts have been made to promote the research & development (R&D) of pouch‐type LMBs toward practical application. This article aims to provide a comprehensive and in‐depth review of recent progress on pouch‐type LMBs from full cell aspect, and to offer insights to guide its future development. It will review pouch‐type LMBs using both liquid and solid‐state electrolytes, and cover topics related to both Li and cathode (including LiNixCoyMn1‐x‐yO2, S and O2) as both electrodes impact the battery performance. The key performance criteria of pouch‐type LMBs and their relationship in between are introduced first, then the major challenges facing the development of pouch‐type LMBs are discussed in detail, especially those severely aggravated in pouch cells compared with coin cells. Subsequently, the recent progress on mechanistic understandings of the degradation of pouch‐type LMBs is summarized, followed with the practical strategies that have been utilized to address these issues and to improve the key performance criteria of pouch‐type LMBs. In the end, it provides perspectives on advancing the R&Ds of pouch‐type LMBs towards their application in practice. [ABSTRACT FROM AUTHOR]

Simultaneous optimization of the energy level of water dissociation, hydrogen and hydroxide desorption is the key to achieving fast kinetics for the alkaline hydrogen evolution reaction (HER). Herein, the well‐dispersed Ru clusters on the surface of amorphous/crystalline CeO2‐δ (Ru/ac‐CeO2‐δ) is demonstrated to be an excellent electrocatalyst for significantly boosting the alkaline HER kinetics owing to the presence of unique oxygen vacancy (VO) and Ru Lewis acid–base pairs (LABPs). The representative Ru/ac‐CeO2‐δ exhibits an outstanding mass activity of 7180 mA mgRu−1 that is approximately 9 times higher than that of commercial Pt/C at the potential of −0.1 V (V vs RHE) and an extremely low overpotential of 21.2 mV at a geometric current density of 10 mA cm−2. Experimental and theoretical studies reveal that the VO as Lewis acid sites facilitate the adsorption of H2O and cleavage of H‐OH bonds, meanwhile, the weak Lewis basic Ru clusters favor for the hydrogen desorption. Importantly, the desorption of OH from VO sites is accelerated via a water‐assisted proton exchange pathway, and thus boost the kinetics of alkaline HER. This study sheds new light on the design of high‐efficiency electrocatalysts with LABPs for the enhanced alkaline HER. [ABSTRACT FROM AUTHOR]