In 1952, the first commercially alkaline Zn||MnO2 primary battery was developed, which is based on Mn4+/Mn3+ redox reactions (MnO2↔Mn2O3). Subsequently, the single-electron (Mn3+/Mn2+ and Mn7+/Mn6+) and two-electron (Mn4+/Mn2+) redox reactions of Mn compound (Mn-Comp) were achieved in aqueous Zn-based batteries. After that, however, the new Mn multivalent change redox reaction was no longer observed. In this study, we report a neutral superhydrophilic hydrogel electrolyte that activates a Mn2+/Mn7+ conversion reaction (Mn2+↔MnO4-). This advance is attributed to an expanding electrochemical stability window and high Mn2+ reaction activity. This enables a discharge plateau of ≥2.2 V in aqueous Zn metal batteries. The high reversibility of Mn2+/Mn7+ conversion reactions during cycling was achieved by incorporating chelation groups in the designed hydrogel electrolyte, which effectively stabilizes the MnO4-. The aqueous Zn||Mn-Comp battery with a 2.2-V discharge plateau operates stably for ≥360 hours.

Cu-based electrocatalysts exhibit superior reduction kinetics in the electrochemical nitrate reduction reaction (NO3RR) and suppress competing hydrogen evolution reaction, making NO3RR an alternative to the traditional Haber-Bosch process in NH3 production. However, the NO3RR in NH3 production involves a nine-proton and eight-electron process, and its performance is constrained by the poor capacity to generate protons. In this study, frustrated Lewis pairs (FLPs) were introduced into Cu-based catalysts to create La-doped Cu2O, in which the FLPs [Cu-O-La-Ov] (where v denotes vacancy) formed by the Lewis acidic sites Ov and Lewis basic sites O in the Cu-O-La motif served as active sites. These active sites facilitated H2O dissociation, providing ample protons for the NO3RR hydrogenation. The La9-CuOx catalyst exhibited an ultralow NH3 production overpotential of only 290 mV, achieving an NH3 current density of 1.76 A cm-2 at -0.4 V vs the reversible hydrogen electrode, with an NH3 yield rate of 139.5 mg h-1 cm-2 and Faradaic efficiency of 98.9%. Due to the superior NO3RR performance of La9-CuOx, a La9-CuOx-based Zn-NO3- battery achieved a remarkable power density of 80.6 mW cm-2, with an NH3 yield rate of 21.4 mg h-1 cm-2. This study clarifies the role of FLPs in facilitating the NO3RR and achieves an efficient Zn-NO3- battery to accomplish electricity generation and NH3 production simultaneously.

The practical applications of aqueous Zn||MnO2 batteries are limited by their small areal capacity, low discharging plateau, and clumsy packing device. Currently, the high potential MnO2/Mn2+ redox conversion can only be well activated in electrolytes with a very low pH value, which is not friendly to the Zn metal anode. To overcome these limitations, we have designed mild amphiphilic hydrogel electrolytes (AHEs) with a wide electrochemical stability window (ESW) and high ionic activity. The design is based on the mechanism that trace amounts of hydrophobic moieties enhance the hydrogen bonding between hydrophilic groups and water molecules in the hydrogel electrolytes. The developed AHE possesses an ESW up to ~3.0 V even at a high water content of ~76 wt%. The assembled Zn||MnO2 pouch cells using the hydrogel electrolytes demonstrated a large areal capacity of ~5 mAh cm-2 at 1 mA cm-2 and a high-voltage and flat discharging plateau of ~1.9 V. Furthermore, a pouch cell with an area of 40 cm2 was fabricated, exhibiting a capacity of ~125 mAh at 2 mA cm-2. Two pouch cells (25 cm2) in series were used to drive a 3.7 V-powerable electric fan. This work highlights the rational design of wide-ESW AHEs with high ionic activity as a promising approach to achieving portable and scalable applications of aqueous high-voltage Zn||MnO2 batteries.

Due to abundant water molecules in conventional aqueous electrolytes and hydrogels, the high activity of water molecules remains a fundamental barrier in zinc batteries (ZBs), especially when operating in aggressive environments (over 60 degrees C). Herein, we design a hydrogel electrolyte via elaborate molecular engineering to optimize ion transport and electrochemical stability. Specifically, the Zn2+ transport can be efficiently expressed under a reduced water content condition with water-assisted functions and flexible polymer chains. Moreover, the decreased water content makes it possible to reduce water reactivity. The Zn||Zn and Zn||Ti batteries can stably and reversibly cycle ('100% Coulombic efficiency) at room temperature and ('99%- Coulombic efficiency) at 90 degrees C, respectively. The full batteries show remarkable cycling stability at room temperature and even at a challenging temperature of 90 degrees C ('100% Coulombic efficiency). This study offers an essential development in environment-adaptable aqueous batteries with highly stable and reversible performances.

Ammonia (NH3) is an important feedstock for industry, an ideal energy carrier, and a perspective storage media for hydrogen. Recently, electrochemical nitrate (NO3-) reduction under acidic conditions has received considerable attention but it suffers from limited efficiency especially under low NO3- concentration. Here, we report an in situ formed positively charged polyethyleneimine-modified Cu under acidic conditions as a catalyst-electrolyte interface (CEI) for electrochemical NO3- reduction to NH3. Such CEI can effectively accumulate NO3- anions via static interactions and accelerate *NO hydrogenation to *NOH by weakening *NO intermediate adsorption on Cu site, thereby facilitating NO3--to-NH3 conversion. Such CEI delivers an increased NH3 Faradaic efficiency (FE) of 83.5% and an impressive half-cell energy efficiency (EE) of 37.1% in 10 mM NO3- solution (pH = 1). The NH3 FE and EE can further increase to 90.2% and 44.1% in 0.5 M NO3-, respectively. The high EE of CEI surpasses previously reported catalyst performances for NO3- reduction. Finally, we demonstrate the feasibility of a novel NO3--furfural battery, showcasing a self-power electrocatalytic system capable of simultaneously treating NO3- pollutants, generating value-added NH3 and upgrading biomass. This work offers valuable insights into the construction of a CEI to enhance the efficiency of NH3 synthesis.

Aqueous Zn batteries (ZBs) are promising candidates for large-scale energy storage, considering their intrinsically safe features, competitive cost, and environmental friendliness. However, the fascinating metallic Zn anode is subjected to severe issues, such as dendrite growth, hydrogen evolution, and corrosion. Additionally, traditional aqueous electrolytes' narrow electrochemical windows and temperature ranges further hinder the practical application of ZBs. Solid-state electrolytes, including solid polymer electrolytes and hydrogel electrolytes, offer distinct paths to mitigate these issues and simultaneously endow the ZBs with customizable functions such as flexibility, self-healing, anti-freezing, and regulated Zn deposition, etc, due to their tuneable structures. This review summarizes the latest progress in developing polymer electrolytes for ZBs, focusing on modifying the ionic conductivity, interfacial compatibility, Zn anode stability, electrochemical stability windows, and improving the environmental adaptability under harsh conditions. Although some achievements are obtained, many critical challenges still exist, and it is hoped to offer guidance for future research, accelerating the development and application of polymer electrolytes.

We propose strategies for sulfur-based cathodes in aqueous zinc-ion batteries, using molecular engineering, adsorption-catalysis, and electrolyte chemistry to boost performance, conductivity, and stability, making them ideal for grid energy storage.