The great interest in fuel cells inspires a substantial amount of research on nonprecious metal catalysts as alternatives to Pt-based oxygen reduction reaction (ORR) electrocatalysts. In this work, bimodal template-based synthesis strategies are proposed for the scalable preparation of hierarchically porous M-N-C (M = Fe or Co) single-atom electrocatalysts featured with active and robust MN 2 active moieties. Multiscale tuning of M-N-C catalysts regarding increasing the number of active sites and boosting the intrinsic activity of each active site is realized simultaneously at a singleatom scale. In addition to the antipoisoning power and high affinity for O 2 , the optimized Fe-N-C catalysts with FeN 2 active site presents a superior electrocatalytic activity for ORR with a half-wave potential of 0.927 V (vs reversible hydrogen electrode (RHE)) in an alkaline medium, which is 49 and 55 mV higher than those of the Co-N-C counterpart and commercial Pt/C, respectively. Density functional theory calculations reveal that the FeN 2 site is more active than the CoN 2 site for ORR due to the lower energy barriers of the intermediates and products involved. The present work may help rational design of more robust ORR electrocatalysts at the atomic level, realizing the significant advances in electrochemical conversion and storage devices. Single-Atom ElectrocatalystsThe ORCID identification number(s) for the author(s) of this article can be found under https://doi.

Sodium (Na) metal is a promising anode for Na-ion batteries. However, the high reactivity of Na metal with electrolytes and the low Na metal cycling efficiency have limited its practical application in rechargeable Na metal batteries. High-concentration electrolytes (HCE, ≥4 M) consisting of sodium bis(fluorosulfonyl)imide (NaFSI) and ether solvent could ensure the stable cycling of Na metal with high Coulombic efficiency but at the cost of high viscosity, poor wettability, and high salt cost. Here, we report that the salt concentration could be significantly reduced (≤1.5 M) by a hydrofluoroether as an "inert" diluent, which maintains the solvation structures of HCE, thereby forming a localized high-concentration electrolyte (LHCE). A LHCE [2.1 M NaFSI/1,2-dimethoxyethane (DME)−bis(2,2,2-trifluoroethyl) ether (BTFE) (solvent molar ratio 1:2)] enables dendrite-free Na deposition with a high Coulombic efficiency of >99%, fast charging (20C), and stable cycling (90.8% retention after 40 000 cycles) of Na∥Na 3 V 2 (PO 4 ) 3 batteries.

To accelerate hydrogel formation and further simplify the synthetic procedure, a series of MCu (M = Pd, Pt, and Au) bimetallic aerogels is synthesized from the in situ reduction of metal precursors through enhancement of the gelation kinetics at elevated temperature. Moreover, the resultant PdCu aerogel with ultrathin nanowire networks exhibits excellent electrocatalytic performance toward ethanol oxidation, holding promise in fuel-cell applications.

search for alternative high energy batteries using abundant and low cost materials is imperative. [2] Sodium ion batteries (SIBs), which as LIBs' close analogy was first explored in the 1980s, have regained substantial spotlights for their great potential as beyond/ post lithium battery chemistry in lowcost electrical energy storage (EES) systems. [3] Being in the same alkaline group with Li, Na chemistry/electrochemistry bears many similarities to Li, hence the SIB development naturally follows the track of success left by LIBs. A variety of cathode/anode pairs and electrolyte have been explored within a short period of time and some of them have been proven to be potentially practical for SIBs. [4] With the understanding deepened, however, it becomes clear that the choice of electrode materials in SIBs and LIBs and their corresponding performance have much less in common than expected, and in many cases even contradictory to each other despite the similarity of the intercalation chemistry between Na-ions and Li-ions.Among the implications ensuing from such differences, the uniqueness of electrode/electrolyte interphases in SIBs profoundly affects the SIBs performances and has not been thoroughly investigated. Such interphases, also known as SEI on anode surface or cathode electrolyte interphase (CEI) on cathode surface, are to a great extent dictated by the chemistry and electrochemistry of Na salts dissolved in aprotic solvent molecules. After the solid electrolyte interphase (SEI)/CEI formation in the initial cycles of SIBs, their chemical/electrochemical reactivity/stability will determine the reversibility and rate of the cell reactions for the rest of the cell life. Solid Electrolyte InterphaseIn battery systems of high voltages such as LIBs, the electrodes operate at potentials outside of the thermodynamic stability limits of the electrolyte. In some cases (but not all), an interphase forms at the interface between electrode (cathode/anode) and electrolyte at the decomposition of the latter, which prevents parasitic reactions and kinetically stabilizes the system. Figure 1A shows a simplified schematic illustration of the anode/cathode surface in LIBs/SIBs with SEI/CEI configuration. The Li/Na ions transport in the bulk electrolyte in the form of solvated ions, and must go through a desolvation process to pass these SEI/CEI into the electrode. Early notions of an ideal SEI layer must possess the general attributes such as: (1) an Sodium-ion batteries (SIBs) as economical, high energy alternatives to lithiumion batteries (LIBs) have received significant attention for large-scale energy storage in the last few years. While the efforts of developing SIBs have benefited from the knowledge learned in LIBs, thanks to the apparent proximity between Na-ions and Li-ions, the unique physical and chemical properties of Na-ions also distinctly differ themselves from Li-ions. It is expected that SIBs have drastically different electrode material structure, solvation-desolvation behavior, electrode-electrolyte interp...

Cobalt‐based bimetallic phosphide encapsulated in carbonized zeolitic imadazolate frameworks has been successfully synthesized and showed excellent activities toward both hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). Density functional theory calculation and electrochemical measurements reveal that the electrical conductivity and electrochemical activity are closely associated with the Co2P/CoP mixed phase behaviors upon Cu metal doping. This relationship is found to be the decisive factor for enhanced electrocatalytic performance. Moreover, the precise control of Cu content in Co‐host lattice effectively alters the Gibbs free energy for H* adsorption, which is favorable for facilitating reaction kinetics. Impressively, an optimized performance has been achieved with mild Cu doping in Cu0.3Co2.7P/nitrogen‐doped carbon (NC) which exhibits an ultralow overpotential of 0.19 V at 10 mA cm–2 and satisfying stability for OER. Cu0.3Co2.7P/NC also shows excellent HER activity, affording a current density of 10 mA cm–2 at a low overpotential of 0.22 V. In addition, a homemade electrolyzer with Cu0.3Co2.7P/NC paired electrodes shows 60% larger current density than Pt/RuO2 couple at 1.74 V, along with negligible catalytic deactivation after 50 h operation. The manipulation of electronic structure by controlled incorporation of second metal sheds light on understanding and synthesizing bimetallic transition metal phosphides for electrolysis‐based energy conversion.

Porous structured silicon has been regarded as a promising candidate to overcome pulverization of silicon-based anodes. However, poor mechanical strength of these porous particles has limited their volumetric energy density towards practical applications. Here we design and synthesize hierarchical carbon-nanotube@silicon@carbon microspheres with both high porosity and extraordinary mechanical strength (>200 MPa) and a low apparent particle expansion of~40% upon full lithiation. The composite electrodes of carbon-nanotube@silicon@carbon-graphite with a practical loading (3 mAh cm −2) deliver~750 mAh g −1 specific capacity, <20% initial swelling at 100% state-of-charge, and~92% capacity retention over 500 cycles. Calendered electrodes achieve~980 mAh cm −3 volumetric capacity density and <50% end-of-life swell after 120 cycles. Full cells with LiNi 1/3 Mn 1/3 Co 1/3 O 2 cathodes demonstrate >92% capacity retention over 500 cycles. This work is a leap in silicon anode development and provides insights into the design of electrode materials for other batteries.

By virtue of diverse structures and tunable properties, metal‐organic frameworks (MOFs) have presented extensive applications including gas capture, energy storage, and catalysis. Recently, synthesis of MOFs and their derived nanomaterials provide an opportunity to obtain competent oxygen reduction reaction (ORR) electrocatalysts due to their large surface area, controllable composition and pore structure. This review starts with the introduction of MOFs and current challenges of ORR, followed by the discussion of MOF‐based non‐precious metal nanocatalysts (metal‐free and metal/metal oxide‐based carbonaceous materials) and their application in ORR electrocatalysis. Current issues in MOF‐derived ORR catalysts and some corresponding strategies in terms of composition and morphology to enhance their electrocatalytic performance are highlighted. In the last section, a perspective for future development of MOFs and their derivatives as catalysts for ORR is discussed.

Self-assembled M-N-doped carbon nanotube aerogels with single-atom catalyst feature are for the first time reported through one-step hydrothermal route and subsequent facile annealing treatment. By taking advantage of the porous nanostructures, 1D nanotubes as well as single-atom catalyst feature, the resultant Fe-N-doped carbon nanotube aerogels exhibit excellent oxygen reduction reaction electrocatalytic performance even better than commercial Pt/C in alkaline solution.