environments, [7-12] where Zn deposition even during shelf time is continuously interfered by competitive hydrogen evolution through H 2 O decomposition (Zn + 2H 2 O → Zn(OH) 2 + H 2) and by consuming both the electrolyte and active Zn metal. This long-neglected problem will remarkably affect calendar life of batteries, which is equivalently important with the intensively studied cycling life of batteries. As revealed in our preliminary quantitative study shown in Figure 1a, immersing Zn in 2 m ZnSO 4 electrolyte will induce an ≈0.25 mmol h-1 cm-2 hydrogen flux. The continuous hydrogen evolution will cause local pH changes, which further induce the formation of loose and brittle Zn 4 SO 4 (OH) 6 •xH 2 O (3Zn(OH) 2 + ZnSO 4 •xH 2 O → Zn 4 SO 4 (OH) 6 •xH 2 O), as revealed in Figure 1b. [13-18] It is generally assumed that these by-products augment the tortuosity and irregularity at the electrode/electrolyte interface with physical contact surface being increased (Figure 1c-h), which will further accelerate hydrogen evolution reaction. The above issues necessitate an effective method to detect hydrogen evolution. Nevertheless, for a Zn-based battery, these assumption and hypotheses are only based on oversimplified observations of battery swelling, gas bubbles, or conducting polarization curve in the absence of Zn 2+ condition, not reflecting physical truth of battery. [19-21] Hydrogen production during electrochemical procedure and even shelf time has not been precisely quantified. Consequently, efforts to make Zn metal a valid anode material may be misdirected. Quantifying the hydrogen production on the electrode during Zn deposition is key to understanding the mechanisms leading to capacity loss and battery failure. On the other hand, these Zn protrusions caused by hydrogen evolution reaction will attract more Zn 2+ flux ("tip" effect) [22] under concentrated electric field during electrochemical cycling, thus accelerating the vertical growth of Zn dendrites instead of planar growth and hydrogen production further flourish (Figure 1g). Up to now, various strategies have been evolved to prohibit the Zn dendrite growth, such as electrolyte optimization, [8,23-25] Zn surface coating, [9,21,26-29] and alloying. [30] To some extent, these strategies stabilize Zn metal, but they do The hydrogen evolution in Zn metal battery is accurately quantified by in situ battery-gas chromatography-mass analysis. The hydrogen fluxes reach 3.76 mmol h −1 cm −2 in a Zn//Zn symmetric cell in each segment, and 7.70 mmol h −1 cm −2 in a Zn//MnO 2 full cell. Then, a highly electronically insulating (0.11 mS cm −1) but highly Zn 2+ ion conductive (80.2 mS cm −1) ZnF 2 solid ion conductor with high Zn 2+ transfer number (0.65) is constructed to isolate Zn metal from liquid electrolyte, which not only prohibits over 99.2% parasitic hydrogen evolution but also guides uniform Zn electrodeposition. Precisely quantitated, the Zn@ZnF 2 //Zn@ZnF 2 cell only produces 0.02 mmol h −1 cm −2 of hydrogen (0.53% of the Zn//Zn cell). Encouragingly, a hig...

A major challenge that prohibits the practical application of single/double-transition metal (3d-M) oxides as oxygen evolution reaction (OER) catalysts is the high overpotentials during the electrochemical process. Herein, our theoretical calculation shows that Fe will be more energetically favorable in the tetrahedral site than Ni and Co, which can further regulate their electronic structure of binary NiCo spinel oxides for optimal adsorption energies of OER intermediates and improved electronic conductivity and hence boost their OER performance. X-ray absorption spectroscopy study on the assynthesized NiCoFe oxide catalysts indicates that Fe preferentially dopes into tetrahedral sites of the lattice, which induces high proportions of Ni 3+ and Co 2+ on the octahedral sites (the active sites in OER). Consequently, this material exhibits a significantly enhanced OER performance with an ultralow overpotential of 201 mV cm −2 at 10 mA cm −2 and a small Tafel slope of 39 mV dec −1 , which are much superior to state-of-the-art Ni−Co based catalysts.

In this study, mechanical vibration is used for hydrogen generation and decomposition of dye molecules, with the help of BiFeO3 (BFO) square nanosheets. A high hydrogen production rate of ≈124.1 μmol g−1 is achieved under mechanical vibration (100 W) for 1 h at the resonant frequency of the BFO nanosheets. The decomposition ratio of Rhodamine B dye reaches up to ≈94.1 % after mechanical vibration of the BFO catalyst for 50 min. The vibration‐induced catalysis of the BFO square nanosheets may be attributed to the piezocatalytic properties of BFO and the high specific surface area of the nanosheets. The uncompensated piezoelectric charges on the surfaces of BFO nanosheets induced by mechanical vibration result in a built‐in electric field across the nanosheets. Unlike a photocatalyst for water splitting, which requires a proper band edge position for hydrogen evolution, such a requirement is not needed in piezocatalytic water splitting, where the band tilting under the induced piezoelectric field will make the conduction band of BFO more negative than the H2/H2O redox potential (0 V) for hydrogen generation.

Proposed are Prussian blue analogue hosts with ordered and continuous channels, and electrocatalytic functionality with open Co and Fe species, which facilitate maximum I2 utilization efficiency and direct I2 to I− conversion kinetics of the I2 reduction reaction, and free up 1/3 I− from I3−. Co[Co1/4Fe3/4(CN)6] exhibits a low energy barrier (0.47 kJ mol−1) and low Tafel slope (76.74 mV dec−1). Accordingly, the Co[Co1/4Fe3/4(CN)6]/I2//Zn battery delivers a capacity of 236.8 mAh g−1 at 0.1 A g−1 and a rate performance with 151.4 mAh g−1 achieved even at 20 A g−1. The battery delivers both high energy density and high‐power density of 305.5 Wh kg−1 and 109.1 kW kg−1, higher than I2//Zn batteries reported to date. Furthermore, solid‐state flexible batteries were constructed. A 100 mAh high capacity solid‐state I2//Zn battery is demonstrated with excellent cycling performance of 81.2 % capacity retained after 400 cycles.

Double-atom catalysts (DACs) have emerged as a novel frontier in heterogeneous catalysis because the synergistic effect between adjacent active sites can promote their catalytic activity while maintaining high atomic utilization efficiency, good selectivity, and high stability originating from the atomically dispersed nature. In this review, the recent progress in both experimental and theoretical research on DACs for various catalytic reactions is focused. Specifically, the central tasks in the design of DACs-manipulating the synergistic effect and engineering atomic and electronic structures of catalysts-are systematically reviewed, along with the prevailing experimental, characterization, and computational modeling approaches. Furthermore, the practical applications of DACs in water splitting, oxygen reduction reaction, nitrogen reduction reaction, and carbon dioxide reduction reaction are addressed. Finally, the future challenges for DACs are summarized and an outlook on the further investigations of DACs toward heterogeneous catalysis in high-performance energy and environmental applications is provided.