Green hydrogen (H₂) has the potential to displace fossil fuels because it has a high energy density, and its consumption yields solely water (H₂O). Water electrolysis generates green H₂, but it is expensive to operate. In conventional water splitting (CWS), hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are closely correlated, producing H₂ and oxygen (O₂) concurrently. Decoupled water splitting (DWS) may geographically and temporally isolate HER from OER. The costly membrane may no longer be necessary. Since 2013, utilizing an auxiliary electrode or redox mediator to separate the rate, time frame, or location of H₂ and O₂ generation during water splitting has been extensively studied. This review provides a comprehensive overview of the latest developments in decoupled water splitting, which offers various benefits over conventional water splitting, including improved safety, higher purity, reduced membrane degradation, and greater design flexibility. The development history, electrolyzer configuration design, improved decoupled water splitting techniques, as well as challenges and future perspectives, are extensively reviewed. We also discuss H₂ generation mechanisms of different DWS technologies, i.e., electron-coupled proton buffers, proton-independent electron reservoirs, electrochemical-thermally activated chemical (E-TAC) water splitting, pseudocapacitors by using soluble molecular redox mediators, insoluble solid-state redox mediators, and hybrid water splitting by integrating oxidative biomass valorization in acidic, alkaline, and neutral environments. Overall, DWS offers promising applications for long-term, renewable energy-driven, viable hydrogen generation from water. Future hydrogen generation from renewable sources may be improved with the help of DWS due to its greater versatility and consistency.

Supercapacitors are at the forefront for powering next-generation electronic devices and offer instantaneous power supply and fast response times. However, the bottleneck lies in designing electrode materials with high capacitance and high energy density. Here, we report a pH-universal RuO₂-based electrocatalytic hydrogen gas capacitor (EHGC). This innovation marks an important leap in pseudocapacitor technology, enabling exceptional chemical stability and catalytic versatility across a wide pH range. This versatility is ascribed to the robustness of RuO₂ and the catalytic properties of hydrogen electrode, resulting in a hybrid system with superior capacitance and energy density. RuO₂-EHGC delivers a high capacitance of 626 F/g and an energy density of 57 Wh/kg at a power density of 200 W/kg in the acidic electrolyte, as well as 80 Wh/kg at 459 W/kg in the alkaline electrolyte at a current density of 1 A/g. Furthermore, RuO₂-EHGC exhibits capacitance retention of 82% after 100,000 cycles at a high current of 30 A/g. The charge storage mechanism is evaluated using ex situ Raman and x-ray photoelectron spectroscopy, which confirms the reversibility of the capacitive charge storage process. This study shows a new approach to the development of high-performance pseudocapacitors, which has the potential to open new avenues of green and sustainable energy storage devices.

Strong interaction between positively charged Mn²⁺ ions and solvent molecules impedes manganese plating process, enabling previous manganese metal batteries non-rechargeable. Now, an innovative halogen-mediated strategy is revealed effective to make manganese metal batteries highly reversible.

Developing facile and economical strategies to fabricate nitrogen-doped porous carbon anode is desirable for dual-carbon potassium ion hybrid capacitors (PIHCs). Here, a high-concentration edge-nitrogen-doped porous carbon (NPC) anode is synthesized by a template-free strategy, in which the total content of pyrrolic nitrogen and pyridinic nitrogen accounts for more than 80% of the nitrogen atoms. As a result, the NPC anode displays a capacity of 315.4 mA h g⁻¹ at a current rate of 0.1 A g⁻¹ and 189.1 mA h g⁻¹ at 5 A g⁻¹. Ex situ characterizations and density functional theory calculations demonstrate the high-concentration edge-nitrogen doping enhances K⁺ adsorption and electronic conductivity of carbon materials, resulting in good electrochemical performance. The assembled NPC//CMK-3 PIHC delivers an energy density of 71.1 W h kg⁻¹ at a power density of 771.9 W kg⁻¹ over 8,000 cycles.

The zinc (Zn) batteries have challenges include uncontrollable dendritic growth, unreasonable negative to positive ratio and limited areal capacity. This highlight presents the latest development to resolve the uncontrollable Zn dendrite formation at high areal capacities of 200 mAh·cm^–2 through a two-dimensional metal/metal-Zn alloy heterostructured interface. The anode-free Zn batteries with an attractive and practical pouch cell energy density of 62 Wh·kg^–1 enlighten an arena towards their commercialization.

With the disruptive carbon cycle being blamed for global warming, the plausible electrocatalytic CO₂ reduction reaction (CO₂RR) to form valuable C₂₊ hydrocarbons and feedstock is becoming a hot topic. Cu-based electrocatalysts have been proven to be excellent CO₂RR alternatives for high energy value-added products in this regard. However, the selectivity of CO₂RR to form C₂₊ products via Cu-based catalysts suffers from a high overpotential, slow reaction kinetics, and low selectivity. This review attempts to discuss various cutting-edge strategies for understanding catalytic design such as Cu-based catalyst surface engineering, tuning Cu bandgap via alloying, nanocatalysis, and the effect of the electrolyte and pH on catalyst morphology. The most recent advances in in situ spectroscopy and computational techniques are summarized to fully comprehend reaction mechanisms, structural transformation/degradation mechanisms, and crystal facet loss with subsequent effects on catalyst activity. Furthermore, approaches for tuning Cu interactions are discussed from four key perspectives: single-atom catalysts, interfacial engineering, metal-organic frameworks, and polymer-incorporated materials, which provide new insights into the selectivity of C₂₊ products. Finally, major challenges are outlined, and potential prospects for the rational design of catalysts for robust CO₂RR are proposed. The integration of catalytic design with mechanistic understanding is a step forward in the promising advancement of CO₂RR technology for industrial applications.

The commercialization of electrolytic MnO₂–Zn batteries is highly applauded owing to the advantages of cost-effectiveness, high safety, high energy density, and durable working performance. However, due to the low reversibility of the cathode MnO₂/Mn²⁺ chemistry at high areal capacities and the severe Zn anode corrosion, the practical application of MnO₂–Zn batteries is hampered by inadequate lifespan. Leveraging the full advantage of an iodine redox mediator, here we design a highly rechargeable electrolytic MnO₂–Zn battery with a high areal capacity. The MnO₂–Zn battery coupled with an iodine mediator in a mild electrolyte shows a high discharge voltage of 1.85 V and a robust areal capacity of 10 mAh cm⁻² under a substantial discharge current density of 160 mA cm⁻². The MnO₂/I₂–Zn battery with an areal capacity of 10 mAh cm⁻² exhibits prolonged stability of over 950 cycles under a high-capacity retention of ~94%. The scaled-up MnO₂/I₂–Zn battery reveals a stable cycle life under a cell capacity of ~600 mAh. Moreover, our constructed MnO₂/I₂–Zn battery demonstrates a practical energy density of ~37 Wh kg⁻¹ and a competitive energy cost of <18 US＄ kWh⁻¹ by taking into account the cathode, anode, and electrolyte. The MnO₂/I₂–Zn battery, with its remarkable reversibility and reasonable energy density, enlightens a new arena of large-scale energy storage devices.