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...