An All-Climate Nonaqueous Hydrogen Gas-Proton Battery.

Rechargeable hydrogen gas batteries, driven by hydrogen evolution and oxidation reactions (HER/HOR), are emerging grid-scale energy storage technologies owing to their low cost and superb cycle life. However, compared with aqueous electrolytes, the HER/HOR activities in nonaqueous electrolytes have rarely been studied. Here, for the first time, we develop a nonaqueous proton electrolyte (NAPE) for a high-performance hydrogen gas-proton battery for all-climate energy storage applications. The advanced nonaqueous hydrogen gas-proton battery (NAHPB) assembled with a representative V2(PO4)3 cathode and H2 anode in a NAPE exhibits a high discharge capacity of 165 mAh g-1 at 1 C at room temperature. It also efficiently operates under all-climate conditions (from -30 to +70 °C) with an excellent electrochemical performance. Our findings offer a new direction for designing nonaqueous proton batteries in a wide temperature range.

Reversible, Dendrite-Free, High-Capacity Aluminum Metal Anode Enabled by Aluminophilic Interface Layer.

Aluminum (Al) metal is an attractive anode material for next-generation rechargeable batteries, because of its low cost and high capacities. However, it brings some fundamental issues such as dendrites, low Coulombic efficiency (CE), and low utilization. Here, we propose a strategy for constructing an ultrathin aluminophilic interface layer (AIL) to regulate the Al nucleation and growth behaviors, which enables highly reversible and dendrite-free Al plating/stripping under high areal capacity. Metallic Al can maintain stable plating/stripping on the Pt-AIL@Ti for over 2000 h at 10 mAh cm-2 with an average CE of 99.9%. The Pt-AIL also enables reversible Al plating/stripping at a record high areal capacity of 50 mAh cm-2, which is 1-2 orders of magnitude higher than the previous studies. This work provides a valuable direction for further construction of high-performance rechargeable Al metal batteries.

Aqueous Organic Hydrogen Gas Proton Batteries with Ultrahigh-Rate and Ultralow-Temperature Performance.

Aqueous proton batteries (APBs) have emerged as one of the most promising batteries for large-scale energy storage technology. However, they usually show an undesirable electrochemical performance. Herein, we demonstrate a novel aqueous catalytic hydrogen gas powered organic proton (HOP) battery, which is driven by hydrogen evolution/oxidation redox reactions via commercial nanocatalysts on the anode and coordination/decoordination reactions of C═O with H+ on the cathode. The HOP battery shows an excellent rate capacity of 190.1 mAh g-1 at 1 A g-1 and 71.4 mAh g-1 at 100 A g-1. It also delivers a capacity of 96.6 mAh g-1 after 100000 cycles and operates at temperatures down to -70 °C. Moreover, the HOP battery is fabricated in a large-scale pouch cell with an extended capacity, exhibiting its potential for practical energy storage applications. This work provides new insights into the building of sustainable APBs, which will broaden the horizons of high-performance aqueous batteries.

Rechargeable Hydrogen-Chlorine Battery Operates in a Wide Temperature Range.

Hydrogen-chlorine (H2-Cl2) fuel cells have distinct merits due to fast electrochemical kinetics but are afflicted by high cost, low efficiency, and poor reversibility. The development of a rechargeable H2-Cl2 battery is highly desirable yet challenging. Here, we report a rechargeable H2-Cl2 battery operating statically in a wide temperature ranging from -70 to 40 °C, which is enabled by a reversible Cl2/Cl- redox cathode and an electrocatalytic H2 anode. A hierarchically porous carbon cathode is designed to achieve effective Cl2 gas confinement and activate the discharge plateau of Cl2/Cl- redox at room temperature, with a discharge plateau at ∼1.15 V and steady cycling for over 500 cycles without capacity decay. Furthermore, the battery operation at an ultralow temperature is successfully achieved in a phosphoric acid-based antifreezing electrolyte, with a reversible discharge capacity of 282 mAh g-1 provided by the highly porous carbon at -70 °C and an average Coulombic efficiency of 91% for more than 300 cycles at -40 °C. This work offers a new strategy to enhance the reversibility of aqueous chlorine batteries for energy storage applications in a wide temperature range.

Facile Fabrication of Bifunctional Hydrogen Catalytic Electrodes for Long-Life Nickel-Hydrogen Gas Batteries.

The renaissance of long-lasting nickel-hydrogen gas (Ni-H2) battery by developing efficient, robust, and affordable hydrogen anode to replace Pt is particularly attractive for large-scale energy storage applications. Here, we demonstrate an extremely facile corrosion induced fabrication approach to achieve a self-supporting hydrogen evolution/oxidation reaction (HER/HOR) bifunctional nanosheet array electrode for Ni-H2 battery. The electrode is constituted by ultrafine Ru nanoparticles on Ni(OH)2 nanosheets grown on nickel foam. Experimental and theoretical calculation results reveal that the electrode with optimized geometric and electronic structures ensures the efficient and robust catalytic hydrogen activities. The fabricated Ni-H2 battery using the Ru-Ni(OH)2/NF anode with an industrial scale areal capacity of 16 mAh cm-2 demonstrates a high energy density, good rate capability and excellent durability without capacity decay over 1800 h. This study casts light on the development of low manufacturing cost and high performance bifunctional hydrogen catalytic electrodes for future hydrogen energy applications.

Descriptor-Driven Computational Design of Bifunctional Double-Atom Hydrogen Evolution and Oxidation Reaction Electrocatalysts for Rechargeable Hydrogen Gas Batteries.

Rechargeable hydrogen gas batteries (RHGBs) have been attracting much attention as promising all-climate large-scale energy storage devices, which calls for low-cost and high-activity hydrogen evolution/oxidation reaction (HER/HOR) bifunctional electrocatalysts to replace the costly platinum-based catalysts. Based on density functional theory (DFT) computations, herein we report an effective descriptor-driven design principle to govern the HER/HOR electrocatalytic activity of double-atom catalysts (DACs) for RHGBs. We systematically investigate the d-band center variation of DACs and their correlations with HER/HOR free energies. We construct activity maps with the d-band center of DACs as a descriptor, which demonstrate that high HER/HOR electrocatalytic activity can be achieved with an appropriate d-band center of DACs. This work not only broadens the applicability of d-band center theory to the prediction of bifunctional HER/HOR electrocatalysts but also paves the way to fast screening and design of efficient and low-cost DACs to promote practical applications of RHGBs.

Surface-Oxygen-Rich Bi@C Nanoparticles for High-Efficiency Electroreduction of CO2 to Formate.

The electrochemical CO2 reduction reaction (CO2RR) is a promising strategy to alleviate excessive CO2 levels in the atmosphere and produce value-added feedstocks and fuels. However, the synthesis of high-efficiency and robust electrocatalysts remains a great challenge. This work reports the green preparation of surface-oxygen-rich carbon-nanorod-supported bismuth nanoparticles (SOR Bi@C NPs) for an efficient CO2RR toward formate. The resultant SOR Bi@C NPs catalyst displays a Faradaic efficiency of more than 91% for formate generation over a wide potential range of 440 mV. Ex situ XPS and XANES and in situ Raman spectroscopy demonstrate that the Bi-O/Bi (110) structure in the pristine SOR Bi@C NPs can remain stable during the CO2RR process. DFT calculations reveal that the Bi-O/Bi (110) structure can facilitate the formation of the *OCHO intermediate. This work provides an approach to the development of high-efficiency Bi-based catalysts for the CO2RR and offers a unique insight into the exploration of advanced electrocatalysts.

An Ultrafast and Ultra-Low-Temperature Hydrogen Gas-Proton Battery.

Aqueous proton batteries are regarded as one of the most promising energy technologies for next-generation grid storage due to the distinctive merits of H+ charge carriers with small ionic radius and light weight. Various materials have been explored for aqueous proton batteries; however, their full batteries show undesirable electrochemical performance with limited rate capability and cycling stability. Here we introduce a novel aqueous proton full battery that shows remarkable rate capability, cycling stability, and ultralow temperature performance, which is driven by a hydrogen gas anode and a Prussian blue analogue cathode in a concentrated phosphoric acid electrolyte. Its operation involves hydrogen evolution/oxidation redox reactions on the anode and H+ insertion/extraction reactions on the cathode, in parallel with the ideal transfer of only H+ between these two electrodes. The fabricated aqueous hydrogen gas-proton battery exhibits an unprecedented charge/discharge capability of up to 960 C with a superior power density of 36.5 kW kg-1, along with an ultralong cycle life of over 0.35 million cycles. Furthermore, this hydrogen gas-proton battery is able to work well at an ultralow temperature of -80 °C with 54% of its room-temperature capacity and under -60 °C with a stable cycle life of 1150 cycles. This work provides new opportunities to construct aqueous proton batteries with high performance in extreme conditions for large-scale energy storage.

Ambient-Stable Two-Dimensional Titanium Carbide (MXene) Enabled by Iodine Etching.

MXene (e.g., Ti3 C2 ) represents an important class of two-dimensional (2D) materials owing to its unique metallic conductivity and tunable surface chemistry. However, the mainstream synthetic methods rely on the chemical etching of MAX powders (e.g., Ti3 AlC2 ) using hazardous HF or alike, leading to MXene sheets with fluorine termination and poor ambient stability in colloidal dispersions. Here, we demonstrate a fluoride-free, iodine (I2 ) assisted etching route for preparing 2D MXene (Ti3 C2 Tx , T=O, OH) with oxygen-rich terminal groups and intact lattice structure. More than 71 % of sheets are thinner than 5 nm with an average size of 1.8 µm. They present excellent thin-film conductivity of 1250 S cm-1 and great ambient stability in water for at least 2 weeks. 2D MXene sheets with abundant oxygen surface groups are excellent electrode materials for supercapacitors, delivering a high gravimetric capacitance of 293 F g-1 at a scan rate of 1 mV s-1 , superior to those made from fluoride-based etchants (<290 F g-1 at 1 mV s-1 ). Our strategy provides a promising pathway for the facile and sustainable production of highly stable MXene materials.

Latest advances in supercapacitors: from new electrode materials to novel device designs.

Notably, many significant breakthroughs for a new generation of supercapacitors have been reported in recent years, related to theoretical understanding, material synthesis and device designs. Herein, we summarize the state-of-the-art progress toward mechanisms, new materials, and novel device designs for supercapacitors. Firstly, fundamental understanding of the mechanism is mainly focused on the relationship between the structural properties of electrode materials and their electrochemical performances based on some in situ characterization techniques and simulations. Secondly, some emerging electrode materials are discussed, including metal-organic frameworks (MOFs), covalent organic frameworks (COFs), MXenes, metal nitrides, black phosphorus, LaMnO3, and RbAg4I5/graphite. Thirdly, the device innovations for the next generation of supercapacitors are provided successively, mainly emphasizing flow supercapacitors, alternating current (AC) line-filtering supercapacitors, redox electrolyte enhanced supercapacitors, metal ion hybrid supercapacitors, micro-supercapacitors (fiber, plane and three-dimensional) and multifunctional supercapacitors including electrochromic supercapacitors, self-healing supercapacitors, piezoelectric supercapacitors, shape-memory supercapacitors, thermal self-protective supercapacitors, thermal self-charging supercapacitors, and photo self-charging supercapacitors. Finally, the future developments and key technical challenges are highlighted regarding further research in this thriving field.

Dual-Graphene Rechargeable Sodium Battery.

Sodium (Na) ion batteries are attracting increasing attention for use in various electrical applications. However, the electrochemical behaviors, particularly the working voltages, of Na ion batteries are substantially lower than those of lithium (Li) ion batteries. Worse, the state-of-the-art Na ion battery cannot meet the demand of miniaturized in modern electronics. Here, we demonstrate that electrochemically exfoliated graphene (EG) nanosheets can reversibly store (PF6- ) anions, yielding high charging and discharging voltages of 4.7 and 4.3 V vs. Na+ /Na, respectively. The dual-graphene rechargeable Na battery fabricated using EG as both the positive and negative electrodes provided the highest operating voltage among all Na ion full cells reported to date, together with a maximum energy density of 250 Wh kg-1 . Notably, the dual-graphene rechargeable Na microbattery exhibited an areal capacity of 35 µAh cm-2 with stable cycling behavior. This study offers an efficient option for the development of novel rechargeable microbatteries with ultra-high operating voltage and high energy density.

A Quasi-Solid-State Li-Ion Capacitor Based on Porous TiO2 Hollow Microspheres Wrapped with Graphene Nanosheets.

The quasi-solid-state Li-ion capacitor is demonstrated with graphene nanosheets prepared by an electrochemical exfoliation as the positive electrode and the porous TiO2 hollow microspheres wrapped with the same graphene nanosheets as the negative electrode, using a Li-ion conducting gel polymer electrolyte. This device may be the key to bridging the gap between conventional lithium-ion batteries and supercapacitors, meanwhile meeting the safety demands of electronic devices.

A Solid-State Electrolyte Based on Li0.95 Na0.05 FePO4 for Lithium Metal Batteries.

Solid-state electrolytes (SSEs) play a crucial role in developing lithium metal batteries (LMBs) with high safety and energy density. Exploring SSEs with excellent comprehensive performance is the key to achieving the practical application of LMBs. In this work, the great potential of Li0.95 Na0.05 FePO4 (LNFP) as an ideal SSE due to its enhanced ionic conductivity and reliable stability in contact with lithium metal anode is demonstrated. Moreover, LNFP-based composite solid electrolytes (CSEs) are prepared to further improve electronic insulation and interface stability. The CSE containing 50 wt% of LNFP (LNFP50) shows high ionic conductivity (3.58 × 10-4 S cm-1 at 25 °C) and good compatibility with Li metal anode and cathodes. Surprisingly, the LMB of Li|LNFP50|LiFePO4 cell at 0.5 C current density shows good cycling stability (151.5 mAh g-1 for 500 cycles, 96.5% capacity retention, and 99.3% Coulombic efficiency), and high-energy LMB of Li|LNFP50|Li[Ni0.8 Co0.1 Mn0.1 ]O2 cell maintains 80% capacity retention after 170 cycles, which are better than that with traditional liquid electrolytes (LEs). This investigation offers a new approach to commercializing SSEs with excellent comprehensive performance for high-performance LMBs.

Electrochemically and Thermally Stable Inorganics-Rich Solid Electrolyte Interphase for Robust Lithium Metal Batteries.

Severe dendrite growth and high-level activity of the lithium metal anode lead to a short life span and poor safety, seriously hindering the practical applications of lithium metal batteries. With a trisalt electrolyte design, an F-/N-containing inorganics-rich solid electrolyte interphase on a lithium anode is constructed, which is electrochemically and thermally stable over long-term cycles and safety abuse conditions. As a result, its Coulombic efficiency can be maintained over 98.98% for 400 cycles. An 85.0% capacity can be retained for coin-type full cells with a 3.14 mAh cm-2 LiNi0.5 Co0.2 Mn0.3 O2 cathode after 200 cycles and 1.0 Ah pouch-type full cells with a 4.0 mAh cm-2 cathode after 72 cycles. During the thermal runaway tests of a cycled 1.0 Ah pouch cell, the onset and triggering temperatures were increased from 70.8 °C and 117.4 °C to 100.6 °C and 153.1 °C, respectively, indicating a greatly enhanced safety performance. This work gives novel insights into electrolyte and interface design, potentially paving the way for high-energy-density, long-life-span, and thermally safe lithium metal batteries.

Non-Noble Metal High-Entropy Alloy-Based Catalytic Electrode for Long-Life Hydrogen Gas Batteries.

The development of efficient, stable, and low-cost bifunctional catalysts for the hydrogen evolution/oxidation reaction (HER/HOR) is critical to promote the application of hydrogen gas batteries in large scale energy storage systems. Here we demonstrate a non-noble metal high-entropy alloy grown on Cu foam (NNM-HEA@CF) as a self-supported catalytic electrode for nickel-hydrogen gas (Ni-H2) batteries. Experimental and theoretical calculation results reveal that the NNM-HEA catalyst greatly facilitates the HER/HOR catalytic process through the optimized electronic structures of the active sites. The assembled Ni-H2 battery with NNM-HEA@CF as the anode shows excellent rate capability and exceptional cycling performance of over 1800 h without capacity decay at an areal capacity of 15 mAh cm-2. Furthermore, a scaled-up Ni-H2 battery fabricated with an extended capacity of 0.45 Ah exhibits a high cell-level energy density of ∼109.3 Wh kg-1. Moreover, its estimated cost reaches as low as ∼107.8 $ kWh-1 based on all key components of electrodes, separator and electrolyte, which is reduced by more than 6 times compared to that of the commercial Pt/C-based Ni-H2 battery. This work provides an approach to develop high-efficiency non-noble metal-based bifunctional catalysts for hydrogen batteries in large-scale energy storage applications.

Ultralow-Temperature Aqueous Conductive Polymer-Hydrogen Gas Battery.

Hydrogen gas batteries are regarded as one of the most promising rechargeable battery systems for large-scale energy storage applications due to their advantages of high rates and long-term cycle lives. However, the development of cost-effective and low-temperature-tolerant hydrogen gas batteries is highly desirable yet very challenging. Herein, we report a novel conductive polymer-hydrogen gas battery that is suitable for ultralow-temperature energy storage applications and consists of a hydrogen gas anode, a conductive polymer cathode using polyaniline (PANI) or polypyrrole as examples, and protonic acidic electrolytes. The PANI-H2 battery using 1 M H2SO4 as the electrolyte exhibits a capacity of 67 mA h/g, a remarkable rate up to 15 A/g, a Coulombic efficiency around 100%, and an ultra-long life of 10,000 cycles. Using the anti-freezing 9 M H3PO4 electrolyte, the PANI-H2 battery can operate well at temperatures down to -70 °C, which maintains ∼70% of the capacity at room temperature and shows an excellent cycle stability under -60 °C. Benefiting from the fast redox kinetics of both electrodes, this work demonstrates excellent rate performance and low-temperature feasibility of conductive polymer-H2 batteries, providing a new avenue for further development of low-cost and reliable polymer-H2 batteries for large-scale energy storage.

pH-Universal Decoupled Water Electrolysis Enabled by Electrocatalytic Hydrogen Gas Capacitive Chemistry.

In conventional water electrolysis (CWE), the H2 and O2 evolution reactions (HER/OER) are tightly coupled, making the generated H2 and O2 difficult to separate, thus resulting in complex separation technology and potential safety issues. Previous efforts on the design of decoupled water electrolysis mainly concentrated on multi-electrode or multi-cell configurations; however, these strategies have the limitation of involving complicated operations. Here, we propose and demonstrate a pH-universal, two-electrode capacitive decoupled water electrolyzer (referred to as all-pH-CDWE) in a single-cell configuration by utilizing a low-cost capacitive electrode and a bifunctional HER/OER electrode to separate H2 and O2 generation for decoupling water electrolysis. In the all-pH-CDWE, high-purity H2 and O2 generation alternately occur at the electrocatalytic gas electrode only by reversing the current polarity. The designed all-pH-CDWE can maintain a continuous round-trip water electrolysis for over 800 consecutive cycles with an electrolyte utilization ratio of nearly 100%. As compared to CWE, the all-pH-CDWE achieves energy efficiencies of 94% in acidic electrolytes and 97% in alkaline electrolytes at a current density of 5 mA cm-2. Further, the designed all-pH-CDWE can be scaled up to a capacity of 720 C in a high current of 1 A for each cycle with a stable HER average voltage of 0.99 V. This work provides a new strategy toward the mass production of H2 in a facilely rechargeable process with high efficiency, good robustness, and large-scale applications.

2D Conjugated Metal-Organic Frameworks Embedded with Iodine for High-Performance Ammonium-Ion Hybrid Supercapacitors.

Ammonium ions (NH4 + ) are emerging non-metallic charge carriers for advanced electrochemical energy storage devices, due to their low cost, elemental abundance, and environmental benignity. However, finding suitable electrode materials to achieve rapid diffusion kinetics for NH4 + storage remains a great challenge. Herein, a 2D conjugated metal-organic framework (2D c-MOF) for immobilizing iodine, as a high-performance cathode material for NH4 + hybrid supercapacitors, is reported. Cu-HHB (HHB = hexahydroxybenzene) MOF embedded with iodine (Cu-HHB/I2 ) features excellent electrical conductivity, highly porous structure, and rich accessible active sites of copper-bis(dihydroxy) (Cu─O4 ) and iodide species, resulting in a remarkable areal capacitance of 111.7 mF cm-2 at 0.4 mA cm-2 . Experimental results and theoretical calculations indicate that the Cu─O4 species in Cu-HHB play a critical role in binding polyiodide and suppressing its dissolution, as well as contributing to a large pseudocapacitance with adsorbed iodide. In combination with a porous MXene anode, the full NH4 + hybrid supercapacitors deliver an excellent energy density of 31.5 mWh cm-2 and long-term cycling stability with 89.5% capacitance retention after 10 000 cycles, superior to those of the state-of-the-art NH4 + hybrid supercapacitors. This study sheds light on the material design for NH4 + storage, enabling the development of novel high-performance energy storage devices.

Anions Regulation Engineering Enables a Highly Reversible and Dendrite-Free Nickel-Metal Anode with Ultrahigh Capacities.

The development of safe and high-energy metal anodes represents a crucial research direction. Here, the achievement of highly reversible, dendrite-free transition metal anodes with ultrahigh capacities by regulating aqueous electrolytes is reported. Using nickel (Ni) as a model, theoretical and experimental evidence demonstrating the beneficial role of chloride ions in inhibiting and disrupting the nickel hydroxide passivation layer on the Ni electrode is provided. As a result, Ni anodes with an ultrahigh areal capacity of 1000 mAh cm-2 (volumetric capacity of ≈6000 mAh cm-3 ), and a Coulombic efficiency of 99.4% on a carbon substrate, surpassing the state-of-the-art metal electrodes by approximately two orders of magnitude, are realized. Furthermore, as a proof-of-concept, a series of full cells based on the Ni anode is developed. The designed Ni-MnO2 full battery exhibits a long lifespan of 2000 cycles, while the Ni-PbO2 full battery achieves a high areal capacity of 200 mAh cm-2 . The findings of this study are important for enlightening a new arena toward the advancement of dendrite-free Ni-metal anodes with ultrahigh capacities and long cycle life for various energy-storage devices.

Ultrafast Electrical Pulse Synthesis of Highly Active Electrocatalysts for Beyond-Industrial-Level Hydrogen Gas Batteries.

The high reliability and proven ultra-longevity make aqueous hydrogen gas (H2 ) batteries ideal for large-scale energy storage. However, the low alkaline hydrogen evolution and oxidation reaction (HER/HOR) activities of expensive platinum catalysts severely hamper their widespread applications in H2 batteries. Here, cost-effective, highly active electrocatalysts, with a model of ruthenium-nickel alloy nanoparticles in ≈3 nm anchored on carbon black (RuNi/C) as an example, are developed by an ultrafast electrical pulse approach for nickel-hydrogen gas (NiH2 ) batteries. Having a competitive low cost of about one fifth of Pt/C benckmark, this ultrafine RuNi/C catalyst displays an ultrahigh HOR mass activity of 2.34 A mg-1 at 50 mV (vs RHE) and an ultralow HER overpotential of 19.5 mV at a current density of 10 mA cm-2 . As a result, the advanced NiH2 battery can efficiently operate under all-climate conditions (from -25 to +50 °C) with excellent durability. Notably, the NiH2 cell stack achieves an energy density up to 183 Wh kg-1 and an estimated cost of ≈49 $ kWh-1 under an ultrahigh cathode Ni(OH)2 loading of 280 mg cm-2 and a low anode Ru loading of ≈62.5 µg cm-2 . The advanced beyond-industrial-level hydrogen gas batteries provide great opportunities for practical grid-scale energy storage applications.