The voltage of carbon-based aqueous supercapacitors is limited by the water splitting reaction occurring in one electrode, generally resulting in the promising but unused potential range of the other electrode. Exploiting this unused potential range provides the possibility for further boosting their energy density. An efficient surface charge control strategy was developed to remarkably enhance the energy density of multiscale porous carbon (MSPC) based aqueous symmetric supercapacitors (SSCs) by controllably tuning the operating potential range of MSPC electrodes. The operating voltage of the SSCs with neutral electrolyte was significantly expanded from 1.4 V to 1.8 V after simple adjustment, enabling the energy density of the optimized SSCs reached twice as much as the original. Such a facile strategy was also demonstrated for the aqueous SSCs with acidic and alkaline electrolytes, and is believed to bring insight in the design of aqueous supercapacitors.

Aqueous rechargeable zinc‐iodine batteries (ZIBs), including zinc‐iodine redox flow batteries and static ZIBs, are promising candidates for future grid‐scale electrochemical energy storage. They are safe with great theoretical capacity, high energy, and power density. Nevertheless, to make aqueous rechargeable ZIBs practically feasible, there are quite a few hurdles that need to be overcome, including self‐discharge, sluggish kinetics, low energy density, and instability of Zn metal anodes. This article first reviews the electrochemistry in aqueous rechargeable ZIBs, including the flow and static battery configurations and their electrode reactions. Then the authors discuss the fundamental questions of ZIBs and highlight the key strategies and recent accomplishments in tackling the challenges. Last, they share their thoughts on the future research development in aqueous rechargeable ZIBs.

Aqueous rechargeable zinc−iodine batteries (ZIBs) are promising candidates for grid energy storage because they are safe and low-cost and have high energy density. However, the shuttling of highly soluble triiodide ions severely limits the device's Coulombic efficiency. Herein, we demonstrate for the first time a double-layered cathode configuration with a conductive layer (CL) coupled with an adsorptive layer (AL) for ZIBs. This unique cathode structure enables the formation and reduction of adsorbed I 3 − ions at the CL/AL interface, successfully suppressing triiodide ion shuttling. A prototypical ZIB using a carbon cloth as the CL and a polypyrrole layer as the AL simultaneously achieves outstanding Coulombic efficiency (up to 95.6%) and voltage efficiency (up to 91.3%) in the aqueous ZnI 2 electrolyte even at high-rate intermittent charging/discharging, without the need of ion selective membranes. These findings provide new insights to the design and fabrication of ZIBs and other batteries based on conversion reactions.

Aqueous rechargeable Ni−Zn battery with high capacity, low cost, and reliable safety has stimulated extensive interests for their promising applications in electric vehicles and portable electronics. The electrochemical properties of electrodes mostly determine the performances of the whole batteries. Currently, the capacities of the most developed cathodes are still far away from that of commercial Zn anode (820 mAh g−1), which is the major barrier for further boosting the energy density of Ni−Zn battery. In recent years, various Ni based materials like α‐Ni(OH)2, β‐Ni(OH)2, NiO and NiCo2O4 have attracted considerable attention and been widely explored as cathode materials for Ni−Zn batteries. However, the poor conductivity and unsatisfactory cyclic stability of Ni‐based materials severely limit their implementation as robust cathodes for Ni−Zn batteries with high energy density and durability. To address these issues, substantial efforts have been made and great processes have been achieved. Herein, we highlight recent advances on rationally structural and componential design of Ni based electrodes for Ni−Zn batteries. The relationships between structures and performances as well as the mechanisms are also discussed. Finally, we present perspectives on the research of next‐generation electrodes with high electrochemical performances.

The voltage of carbon‐based aqueous supercapacitors is limited by the water splitting reaction occurring in one electrode, generally resulting in the promising but unused potential range of the other electrode. Exploiting this unused potential range provides the possibility for further boosting their energy density. An efficient surface charge control strategy was developed to remarkably enhance the energy density of multiscale porous carbon (MSPC) based aqueous symmetric supercapacitors (SSCs) by controllably tuning the operating potential range of MSPC electrodes. The operating voltage of the SSCs with neutral electrolyte was significantly expanded from 1.4 V to 1.8 V after simple adjustment, enabling the energy density of the optimized SSCs reached twice as much as the original. Such a facile strategy was also demonstrated for the aqueous SSCs with acidic and alkaline electrolytes, and is believed to bring insight in the design of aqueous supercapacitors.

Aqueous rechargeable nickel–zinc batteries are highly attractive for large-scale energy storage for their high output voltage, low cost, and excellent safety; however, their inferior cycling durability due to the degradation of the Ni-based cathode is a major obstacle for their applications. In this context, we develop a new kind of porous electrochemically activated Ni nanoparticle/nitrogen-doped carbon (Ni/NC) composite material as ultrastable cathodes for advanced aqueous rechargeable nickel–zinc batteries. The in situ formation of a highly active NiO x (OH) y layer on Ni nanoparticles and a unique hydrophilic porous architecture endow the activated Ni/NC composite with high accessible area, abundant active sites, easy electrolyte permeation, and shortened charge/ion transport pathway. Consequently, a high capacity of 381.2 μAh cm–3 with an outstanding rate capability is achieved by the Ni–Zn battery using the optimized activated Ni/NC composite as the cathode (about 30-fold enhancement compared to that with the pristine Ni/NC composite as the cathode). More impressively, the as-assembled Ni–Zn battery achieves an unprecedented cyclic stability with no capacity loss after 36 000 charge/discharge cycles. This is the highest cyclic durability ever for Ni–Zn batteries and other aqueous rechargeable batteries. This novel efficient electrochemical activation strategy to achieve a high-performance cathode and demonstration of an ultrastable aqueous rechargeable Ni–Zn battery may open up new vistas on the development of more advanced and reliable energy storage materials and devices.

This article discusses the power of coupling experiments with DFT in obtaining insights into the fundamentals of HER, Qincluding explaining experimental results and revealing reaction mechanisms and facilitating the development of new HER electrocatalysts.

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