Hydrogen peroxide (H2O2) synthesis generally requires substantial postreaction purification. Here, we report a direct electrosynthesis strategy that delivers separate hydrogen (H2) and oxygen (O2) streams to an anode and cathode separated by a porous solid electrolyte, wherein the electrochemically generated H+ and HO2 – recombine to form pure aqueous H2O2 solutions. By optimizing a functionalized carbon black catalyst for two-electron oxygen reduction, we achieved >90% selectivity for pure H2O2 at current densities up to 200 milliamperes per square centimeter, which represents an H2O2 productivity of 3.4 millimoles per square centimeter per hour (3660 moles per kilogram of catalyst per hour). A wide range of concentrations of pure H2O2 solutions up to 20 weight % could be obtained by tuning the water flow rate through the solid electrolyte, and the catalyst retained activity and selectivity for 100 hours

Electrocatalytic CO2 reduction is often carried out in a solution electrolyte such as KHCO3(aq), which allows for ion conductionbetween electrodes. Therefore, liquid products that form are in a mixture with the dissolved salts, requiring energy-intensivedownstream separation. Here, we report continuous electrocatalytic conversion of CO2 to pure liquid fuel solutions in cells thatutilize solid electrolytes, where electrochemically generated cations (such as H+) and anions (such as HCOO−) are combinedto form pure product solutions without mixing with other ions. Using a HCOOH-selective (Faradaic efficiencies > 90%) andeasily scaled Bi catalyst at the cathode, we demonstrate production of pure HCOOH solutions with concentrations up to 12 M.We also show 100 h continuous and stable generation of 0.1 M HCOOH with negligible degradation in selectivity and activity.Production of other electrolyte-free C2+ liquid oxygenate solutions, including acetic acid, ethanol and n-propanol, are also demonstrated using a Cu catalyst. Finally, we show that our CO2 reduction cell with solid electrolytes can be modified to suit other,more complex practical applications.

Shifting electrochemical oxygen reduction towards 2e– pathway to hydrogen peroxide(H2O2), instead of the traditional 4e– to water, becomes increasingly important as a greenmethod for H2O2 generation. Here, through a flexible control of oxygen reduction pathwayson different transition metal single atom coordination in carbon nanotube, we discovered FeC-O as an efficient H2O2 catalyst, with an unprecedented onset of 0.822 V versus reversiblehydrogen electrode in 0.1 M KOH to deliver 0.1 mA cm−2 H2O2 current, and a high H2O2selectivity of above 95% in both alkaline and neutral pH. A wide range tuning of 2e–/4e– ORRpathways was achieved via different metal centers or neighboring metalloid coordination.Density functional theory calculations indicate that the Fe-C-O motifs, in a sharp contrast tothe well-known Fe-C-N for 4e–, are responsible for the H2O2 pathway. This iron single atomcatalyst demonstrated an effective water disinfection as a representative application.

Vanadium-based compounds have been widely used aselectrode materials in aqueous zinc ion batteries (ZIBs) due to themultiple oxidation states of vanadium and their open frameworkstructure. However, the solubility of vanadium in aqueous electrolytes and the formation of byproducts during the charge/dischargeprocess cause severe capacity fading and limit cycle life. Here, wereport an ultrathin HfO2 film as an artificial solid electrolyteinterphase (SEI) that is uniformly and conformally deposited byatomic layer deposition (ALD). The inactive hafnium(IV) oxide(HfO2) film not only decreases byproduct (Zn4SO4(OH)6·xH2O)formation on the surface of Zn3V2O7(OH)2·2H2O (ZVO) but alsosuppresses the ZVO cathode dissolution in the electrolyte. As aresult, the obtained HfO2-coated ZVO cathodes deliver highercapacity and better cycle life (227 mAh g−1@100 mA g−1, 90% retention over 100 cycles) compared with pristine ZVO(170 mAh g−1@100 mA g−1, 45% retention over 100 cycles). A mechanistic investigation of the role of HfO2 is presented,along with data showing that our method constitutes a general strategy for other cathodes to enhance their performancein aqueous ZIBs

Pseudocapacitance is generally associated with either surface redox reactions or ion intercalation processeswithout a phase transition. Typically, these two mechanisms have been independently studied, and most workshave focused on optimizing one or the other in different material systems. Here we have developed a strategybased on solubility contrast, in which the contribution from the two capacitive mechanisms is simultaneouslyoptimized. Taking layered birnessite MnO2 as a model, controllable nanostructures and oxygen vacancies areachieved through a simple coprecipitation process. Simultaneously controlling crystallite size and defect concentration is shown to enhance the charging-discharging kinetics together with both redox and intercalationcapacitances. This synergistic effect results from enhanced ionic diffusion, electronic conductivity, and largesurface-to-volume ratio. In addition, considerable cycling durability is achieved, resulting from improved framework strength by defect creation and the absence of proton (de)intercalation during discharge/charge. Thiswork underscores the importance of synergistically regulating nanostructure and defects in redox-active materials to improve pseudocapacitive charge storage.

The increasing global demand for energy and the potential environmental impact of increased energy consumption require greener, safer, and more cost-efficient energy storage technologies. Lithium-ion batteries (LIBs)have been successful in meeting much of today’s energy storage demand; however, lithium (Li) is a costly metal,is unevenly distributed around the world, and poses serious safety and environmental concerns. Alternate battery technologies should thus be developed. Zinc-ion batteries (ZIBs) have recently attracted attention due totheir safety, environmental friendliness, and lower cost, compared to LIBs. They use aqueous electrolytes, whichgive them an advantage over multivalent ion batteries (e.g., Mg2+, Ca2+, Al3+) that require more complexelectrolytes. However, as with every new technology, many fundamental and practical challenges must beovercome for ZIBs to become commercial products. In this manuscript, we present a timely review and offerperspectives on recent developments and future directions in ZIBs research. The review is divided into five parts:(i) cathode material development, including an understanding of their reaction mechanism; (ii) electrolytedevelopment and characterization; (iii) zinc anode, current collector, and separator design; (iv) applications; and(v) outlook and perspective.

Microsupercapacitors (MSCs) with high energy densities offer viable minia-turized alternatives to bulky electrolytic capacitors if the former can respond at the kilo Hertz (kHz) or higher frequencies. Moreover, MSCs fabricated on a chip can be integrated into thin-film electronics in a compatible manner, serving the function of ripple filtering units or harvesters of energy from high-frequency sources. In this work, wafer-scale fabrication is demonstrated of MXene microsupercapacitors with controlled flake sizes and engineered device designs to achieve excellent frequency filtering performance. Specifi-cally, the devices (100 nm thick electrodes and 10 µm interspace) deliver high volumetric capacitance (30 F cm−3 at 120 Hz), high rate capability (300 V s−1), and a very short relaxation time constant (τ = 0.45 ms), surpassing conven-tional electrolytic capacitors (τ = 0.8 ms). As a result, the devices are capable of filtering 120 Hz ripples produced by AC line power at a frequency of 60 Hz. This study opens new avenues for exploring miniaturized MXene MSCs as replacements for bulky electrolytic capacitors