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

Aqueous Zinc-Chlorine Battery Modulated by a MnO2 Redox Adsorbent

Aqueous zinc-chlorine battery with high discharge voltage and attractive theoretical energy density is expected to become an important technology for large-scale energy storage. However, the practical application of Zn-Cl2 batteries has been restricted due to the Cl2 cathode with sluggish kinetics and low Coulombic efficiency (CE). Here, an aqueous Zn-Cl2 battery using an inexpensive and effective MnO2 redox adsorbent (referred to Zn-Cl2@MnO2 battery) to modulate the electrochemical performance of the Cl2 cathode is developed. Density functional theory calculations reveal that the existence of the intermediate state Clads free radical catalyzed by MnO2 on the Cl2 cathode contributes to the charge storage capacity, which is the key to modulate the electrode and improve the electrochemical performance. Further analysis of the Cl2 cathode kinetics discloses the adsorption and catalytic roles of the MnO2 redox adsorbent. The Zn-Cl2@MnO2 battery displays an enhanced discharge voltage of 2.0 V at a current density of 2.5 mA cm-2, and stable 1000 cycles with an average CE of 91.6%, much superior to the conventional Zn-Cl2 battery with an average CE of only 66.8%. The regulation strategy to the Cl2 cathode provides opportunities for the future development of aqueous Zn-Cl2 batteries.

Observation of super-Nernstian proton-coupled electron transfer and elucidation of nature of charge carriers in a multiredox conjugated polymer

Nernstian proton-coupled electron transfer (PCET) is a fundamental process central to many physical and biological systems, such as electrocatalysis, enzyme operation, DNA biosynthesis, pH-/bio-sensors, and electrochemical energy storage devices. We report herein the discovery of super-Nernstian PCET behavior with two protons per electron transferred in the electrochemical doping of a redox conjugated polymer, phenazine-substituted ladder poly(benzimidazobenzophenanthroline) (BBL-P), in aqueous electrolyte. We show that the super-Nernstian response originates from existence of multiredox centers that have a gradient of pKa on the conjugated polymer. Our use of various pH-dependent in operando techniques to probe the nature of charge carriers in n-doped BBL-P found that polarons are the charge carriers at low to intermediate levels of doping (0.1-1.0 electron per repeat unit (eru)) whereas at higher doing levels (1.3 eru), polarons, polaron pairs, and bipolarons co-exist, which evolve into strongly coupled polaron pairs at the highest doping levels (>1.5 eru). We show that PCET-assisted n-doping of BBL-P results in very high redox capacity (>1200 F cm-3) in acidic electrolyte. Our results provide important new insights into PCET in organic materials and the nature of charge carriers in n-doped conjugated polymers while having implications for various electrochemical devices.

Decoupled electrolysis for hydrogen production and hydrazine oxidation via high-capacity and stable pre-protonated vanadium hexacyanoferrate

Decoupled electrolysis for hydrogen production with the aid of a redox mediator enables two half-reactions operating at different rates, time, and spaces, which offers great flexibility in operation. Herein, a pre-protonated vanadium hexacyanoferrate (p-VHCF) redox mediator is synthesized. It offers a high reversible specific capacity up to 128 mAh g-1 and long cycling performance of 6000 cycles with capacity retention about 100% at a current density of 10 A g-1 due to the enhanced hydrogen bonding network. By using this mediator, a membrane-free water electrolytic cell is built to achieve decoupled hydrogen and oxygen production. More importantly, a decoupled electrolysis system for hydrogen production and hydrazine oxidation is constructed, which realizes not only separate hydrogen generation but electricity generation through the p-VHCF-N2H4 liquid battery. Therefore, this work enables the flexible energy conversion and storage with hydrogen production driven by solar cell at day-time and electricity output at night-time.

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.

Recent advances in battery characterization using in situ XAFS, SAXS, XRD, and their combining techniques: From single scale to multiscale structure detection

Revealing and clarifying the chemical reaction processes and mechanisms inside the batteries will bring a great help to the controllable preparation and performance modulation of batteries. Advanced characterization techniques based on synchrotron radiation (SR) have accelerated the development of various batteries over the past decade. In situ SR techniques have been widely used in the study of electrochemical reactions and mechanisms due to their excellent characteristics. Herein, the three most wide and important synchrotron radiation techniques used in battery research were systematically reviewed, namely X-ray absorption fine structure (XAFS) spectroscopy, small-angle X-ray scattering (SAXS), and X-ray diffraction (XRD). Special attention is paid to how these characterization techniques are used to understand the reaction mechanism of batteries and improve the practical characteristics of batteries. Moreover, the in situ combining techniques advance the acquisition of single scale structure information to the simultaneous characterization of multiscale structures, which will bring a new perspective to the research of batteries. Finally, the challenges and future opportunities of SR techniques for battery research are featured based on their current development.

Rechargeable Li/Cl2 Battery Down to -80 °C

Low temperature rechargeable batteries are important to life in cold climates, polar/deep-sea expeditions, and space explorations. Here, this work reports 3.5-4 V rechargeable lithium/chlorine (Li/Cl2 ) batteries operating down to -80 °C, employing Li metal negative electrode, a novel carbon dioxide (CO2 ) activated porous carbon (KJCO2 ) as the positive electrode, and a high ionic conductivity (≈5-20 mS cm-1 from -80 °C to room-temperature) electrolyte comprised of aluminum chloride (AlCl3 ), lithium chloride (LiCl), and lithium bis(fluorosulfonyl)imide (LiFSI) in low-melting-point (-104.5 °C) thionyl chloride (SOCl2 ). Between room-temperature and -80 °C, the Li/Cl2 battery delivers up to ≈29 100-4500 mAh g-1 first discharge capacity (based on carbon mass) and a 1200-5000 mAh g-1 reversible capacity over up to 130 charge-discharge cycles. Mass spectrometry and X-ray photoelectron spectroscopy probe Cl2 trapped in the porous carbon upon LiCl electro-oxidation during charging. At -80 °C, Cl2 /SCl2 /S2 Cl2 generated by electro-oxidation in the charging step are trapped in porous KJCO2 carbon, allowing for reversible reduction to afford a high discharge voltage plateau near ≈4 V with up to ≈1000 mAh g-1 capacity for SCl2 /S2 Cl2 reduction and up to ≈4000 mAh g-1 capacity at ≈3.1 V plateau for Cl2 reduction.

Vanadium Hexacyanoferrate Prussian Blue Analogs for Aqueous Proton Storage: Excellent Electrochemical Properties and Mechanism Insights

The significant attraction toward aqueous proton batteries (APBs) is attributable to their expedited kinetics, elevated safety profile, and economical feasibility. Nevertheless, their practical implement is significantly blocked by the unsatisfactory energy density due to the limited cathode materials. Herein, vanadium hexacyanoferrate Prussian blue analog (VOHCF) is introduced as a potentially favorable cathode material for APBs. The findings demonstrate that this VOHCF electrode exhibits a notable reversible capacity of 102.7 mAh g-1 and exceptional cycling stability, with 95.4% capacity retention over 10 000 cycles at 10 A g-1 . It is noteworthy that this is the detailed instance of VOHCF being proposed as a cathode for APBs. Combining the in situ characterization techniques and theoretical simulations, the origins of excellent proton storage performance are revealed as the multiple redox mechanisms with double active centers of ─C≡N group and V═O bond in VOHCF as well as the robust structure stability. A proton full cell with excellent performance is further achieved by coupling the VOHCF cathode and diquinoxalino[2,3-a:2',3'-c] phenazine (HATN) anode, demonstrating the great potential of VOHCF in practical applications. This work could provide fundamental understanding to the development of feasible cathode materials for proton storage device.

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.

Proton Intercalation/De-intercalation Chemistry in Phenazine-based Anode for Hydronium-ion Batteries

Hydronium-ion batteries have received significant attention owing to the merits of extraordinary sustainability and excellent rate abilities. However, achieving high-performance hydronium-ion batteries remains a challenge due to the inferior properties of anode materials in strong acid electrolyte. Herein, a hydronium-ion battery is constructed which is based on a diquinoxalino [2,3-a:2',3'-c] phenazine (HATN) anode and a MnO2 @graphite felt cathode in a hybrid acidic electrolyte. The fast kinetics of hydronium-ion insertion/extraction into HATN electrode endows the HATN//MnO2 @GF battery with enhanced electrochemical performance. This battery exhibits an excellent rate performance (266 mAh g-1 at 0.5 A g-1 , 97 mAh g-1 at 50 A g-1 ), attractive energy density (182.1 Wh kg-1 ) and power density (31.2 kW kg-1 ), along with long-term cycle stability. These results shed light on the development of advanced hydronium-ion batteries.

Quinone-amine polymer nanospheres with enhanced redox activity for aqueous proton storage

One of the biggest obstacles to the development of aqueous proton batteries (APBs), despite numerous optimization techniques, is the preparation and use of high-performance electrode materials. In this work, to improve the high solubility, limited capacity and poor cycle life of small organic molecules in APBs, homogeneous dispersed quinone-amine polymer nanospheres (PQANS) (average diameter: 220 nm) were synthesized by a polymerization reaction based on 3,3'-diaminobenzidine (DAB) and benzoquinone (BQ), making them suitable for proton storage in aqueous systems. As an anode for APBs, the obtained PQANS exhibits an improved reversible capacity of 126.2 mAh/g at 1 A/g after 300 cycles. The durable stable measurement of PQANS at 10 A/g was also conducted with a specific capacity of 66.8 mAh/g after 12,000 cycles. A series of in situ or ex situ measurements were used to establish the superior H+ storage mechanism of PQANS. A novel reaction mechanism of redox enhancement was revealed due to the existence of more carbonyl groups after the first cycle. Theoretical calculations were conducted to help illustrate the principle of binding protons with functional groups in PQANS. Finally, a PQANS anode-based aqueous proton full battery was constructed to demonstrate its potential application, which exhibits a specific capacity of 50.6 mAh/g at 1 A/g (600 cycles). This work provides a reference for preparing high-performance polymer-based electrode materials in aqueous 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.

Discovery of a three-proton insertion mechanism in α-molybdenum trioxide leading to enhanced charge storage capacity

The α-molybdenum trioxide has attracted much attention for proton storage owing to its easily modified bilayer structure, fast proton insertion kinetics, and high theoretical specific capacity. However, the fundamental science of the proton insertion mechanism in α-molybdenum trioxide has not been fully understood. Herein, we uncover a three-proton intercalation mechanism in α-molybdenum trioxide using a specially designed phosphoric acid based liquid crystalline electrolyte. The semiconductor-to-metal transition behavior and the expansion of the lattice interlayers of α-molybdenum trioxide after trapping one mole of protons are verified experimentally and theoretically. Further investigation of the morphology of α-molybdenum trioxide indicates its fracture behavior upon the proton intercalation process, which creates diffusion channels for hydronium ions. Notably, the observation of an additional redox behavior at low potential endows α-molybdenum trioxide with an improved specific discharge capacity of 362 mAh g-1.

Ultrahigh-rate and ultralong-life aqueous batteries enabled by special pair-dancing proton transfer

The design of Faradaic battery electrodes with high rate capability and long cycle life comparable to those of supercapacitors is a grand challenge. Here, we bridge this performance gap by taking advantage of a unique ultrafast proton conduction mechanism in vanadium oxide electrode, developing an aqueous battery with untrahigh rate capability up to 1000 C (400 A g^-1) and extremely long life of 0.2 million cycles. The mechanism is elucidated by comprehensive experimental and theoretical results. Instead of slow individual Zn²⁺ transfer or Grotthuss chain transfer of confined H⁺, the ultrafast kinetics and excellent cyclic stability are enabled by rapid 3D proton transfer in vanadium oxide via the special pair dance switching between Eigen and Zundel configurations with little constraint and low energy barriers. This work provides insight into developing high-power and long-life electrochemical energy storage devices with nonmetal ion transfer through special pair dance topochemistry dictated by hydrogen bond.

An Internal Real-Time Microscopic Diagnosis of a Proton Battery Stack during Charging and Discharging

The proton battery has facilitated a new research direction for technologies related to fuel cells and energy storage. Our R&D team has developed a prototype of a proton battery stack, but there are still problems to be solved, such as leakage and unstable power generation. Moreover, it is unlikely that the multiple important physical parameters inside the proton battery stack can be measured accurately and simultaneously. At present, external or single measurements represent the bottleneck, yet the multiple important physical parameters (oxygen, hydrogen, voltage, current, temperature, flow, and humidity) are interrelated and have a significant impact on the performance, life, and safety of the proton battery stack. This research uses micro-electro-mechanical systems (MEMS) technology to develop a micro oxygen sensor and integrates the six-in-one microsensor that our R&D team previously developed in order to improve sensor output and facilitate overall operation by redesigning the incremental mask and having this co-operate with a flexible board for sensor back-end integration, completing the development of a flexible seven-in-one (oxygen, hydrogen, voltage, current, temperature, flow, and humidity) microsensor.

Solid-Liquid-Gas Management for Low-Cost Hydrogen Gas Batteries

Aqueous nickel-hydrogen gas (Ni-H₂) batteries with excellent durability (>10,000 cycles) are important candidates for grid-scale energy storage but are hampered by the high-cost Pt electrode with limited performance. Herein, we report a low-cost nickel-molybdenum (NiMo) alloy as an efficient bifunctional hydrogen evolution and oxidation reaction (HER/HOR) catalyst for Ni-H₂ batteries in alkaline electrolytes. The NiMo alloy demonstrates a high HOR mass-specific kinetic current of 28.8 mA mg^-1 at 50 mV as well as a low HER overpotential of 45 mV at a current density of 10 mA cm^-2, which is better than most nonprecious metal catalysts. Furthermore, we apply a solid-liquid-gas management strategy to constitute a conductive, hydrophobic network of NiMo using multiwalled carbon nanotubes (NiMo-hydrophobic MWCNT) in the electrode to accelerate HER/HOR activities for much improved Ni-H₂ battery performance. As a result, Ni-H₂ cells based on the NiMo-hydrophobic MWCNT electrode show a high energy density of 118 Wh kg^-1 and a low cost of only 67.5 $ kWh^-1. With the low cost, high energy density, excellent durability, and improved energy efficiency, the Ni-H₂ cells show great potential for practical grid-scale energy storage.

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.

Anhydrous Superprotonic Conductivity in the Zirconium Acid Triphosphate ZrH5 (PO4 )3

The development of solid-state proton conductors with high proton conductivity at low temperatures is crucial for the implementation of hydrogen-based technologies for portable and automotive applications. Here, we report on the discovery of a new crystalline metal acid triphosphate, ZrH₅ (PO₄ )₃ (ZP3), which exhibits record-high proton conductivity of 0.5-3.1×10^-2  S cm^-1 in the range 25-110 °C in anhydrous conditions. This is the highest anhydrous proton conductivity ever reported in a crystalline solid proton conductor in the range 25-110 °C. Superprotonic conductivity in ZP3 is enabled by extended defective frustrated hydrogen bond chains, where the protons are dynamically disordered over two oxygen centers. The high proton conductivity and stability in anhydrous conditions make ZP3 an excellent candidate for innovative applications in fuel cells without the need for complex water management systems, and in other energy technologies requiring fast proton transfer.

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.

High-Capacity Zinc Anode with 96 % Utilization Rate Enabled by Solvation Structure Design

Aqueous zinc-ion batteries (AZBs) show promises for large-scale energy storage. However, the zinc utilization rate (ZUR) is generally low due to side reactions in the aqueous electrolyte caused by the active water molecules. Here, we design a novel solvation structure in the electrolyte by introduction of sulfolane (SL). Theoretical calculations, molecular dynamics simulations and experimental tests show that SL remodels the primary solvation shell of Zn²⁺ , which significantly reduces the side reactions of Zn anode and achieves high ZUR under large capacities. Specifically, the symmetric and asymmetric cells could achieve a maximum of ∼96 % ZUR at an areal capacity of 24 mAh cm^-2 . In a ZUR of ∼67 %, the developed Zn-V₂ O₅ full cell can be stably cycled for 500 cycles with an energy density of 180 Wh kg^-1 and Zn-AC capacitor is stable for 5000 cycles. This electrolyte structural engineering strategy provides new insight into achieving high ZUR of Zn anodes for high performance AZBs.

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.

An Amorphous Anode for Proton Battery

Developing advanced electrode materials is crucial for improving the electrochemical performances of proton batteries. Currently, the anodes are primarily crystalline materials which suffer from inferior cyclic stability and high electrode potential. Herein, we propose amorphous electrode materials for proton batteries by using a general ion-exchange protocol to introduce multivalent metal cations for activating the host material. Taking Al3+ as an example, theoretical and experimental analysis demonstrates electrostatic interaction between metal cations and lattice oxygen, which is the primary barrier for direct introduction of the multivalent cations, is effectively weakened through ion exchange between Al3+ and pre-intercalated K+. The as-prepared Al-MoOx anode therefore delivered a remarkable capacity and outstanding cycling stability that outperforms most of the state-of-the-art counterparts. The assembled full cell also achieved a high voltage of 1.37 V. This work opens up new opportunities for developing high-performance electrodes of proton batteries by introducing amorphous materials.

High-Energy and Long-Lived Zn-MnO2 Battery Enabled by a Hydrophobic-Ion-Conducting Membrane

Alkaline Zn-MnO₂ batteries feature high security, low cost, and environmental friendliness while suffering from severe electrochemical irreversibility for both the Zn anode and MnO₂ cathode. Although neutral electrolytes are supposed to improve the reversibility of the Zn anode, the MnO₂ cathode indeed experiences a capacity degradation caused by the Jahn-Teller effect of the Mn³⁺ ion, thus shortening the lifespan of the neutral Zn-MnO₂ batteries. Theoretically, the MnO₂ cathode undergoes a highly reversible two-electron redox reaction of the MnO₂/Mn²⁺ couple in strongly acidic electrolytes. However, acidic electrolytes would inevitably accelerate the corrosion of the Zn anode, making long-lived acidic Zn-MnO₂ batteries impossible. Herein, to overcome the challenges faced by Zn-MnO₂ batteries, we propose a hybrid Zn-MnO₂ battery (HZMB) by coupling the neutral Zn anode with the acidic MnO₂ cathode, wherein the neutral anode and acidic cathode are separated by a proton-shuttle-shielding and hydrophobic-ion-conducting membrane. Benefiting from the optimized reaction conditions for both the MnO₂ cathode and Zn anode as well as the well-designed membrane, the HZMB exhibits a high working voltage of 2.05 V and a long lifespan of 2275 h (2000 cycles), breaking through the limitations of Zn-MnO₂ batteries in terms of voltage and cycle life.

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.

Rechargeable Batteries for Grid Scale Energy Storage

Ever-increasing global energy consumption has driven the development of renewable energy technologies to reduce greenhouse gas emissions and air pollution. Battery energy storage systems (BESS) with high electrochemical performance are critical for enabling renewable yet intermittent sources of energy such as solar and wind. In recent years, numerous new battery technologies have been achieved and showed great potential for grid scale energy storage (GSES) applications. However, their practical applications have been greatly impeded due to the gap between the breakthroughs achieved in research laboratories and the industrial applications. In addition, various complex applications call for different battery performances. Matching of diverse batteries to various applications is required to promote practical energy storage research achievement. This review provides in-depth discussion and comprehensive consideration in the battery research field for GSES. The overall requirements of battery technologies for practical applications with key parameters are systematically analyzed by generating standards and measures for GSES. We also discuss recent progress and existing challenges for some representative battery technologies with great promise for GSES, including metal-ion batteries, lead-acid batteries, molten-salt batteries, alkaline batteries, redox-flow batteries, metal-air batteries, and hydrogen-gas batteries. Moreover, we emphasize the importance of bringing emerging battery technologies from academia to industry. Our perspectives on the future development of batteries for GSES applications are provided.

Novel Urea-Based Molecule Functioning as a Solid Electrolyte Interphase Enabler and LiPF6 Decomposition Inhibitor for Fast-Charging Lithium Metal Batteries

The practical application of lithium metal batteries is impeded by the growth of dendrites and decomposition of electrolytes especially at high temperature in normal carbonate-based electrolytes. Herein, a novel urea-based molecule, 1,3-dimethyl-2-imidazolidinone (DMI), with a high donor number is proposed, which exhibits an extraordinary solubility of LiNO₃ of over 5 M. As a result, a sufficient amount of LiNO₃ is readily introduced into the carbonate electrolytes with DMI as an additive, and an average coulombic efficiency of 99.1% for lithium plating/stripping is achieved due to a stable solid electrolyte interphase (SEI) rich in inorganic-rich lithium salts. The Li||Li symmetric cell achieves a stable operation for over 2500 h at 0.5 mA cm^-2 and 1 mAh cm^-2, and a granular shape of deposited Li metal is still preserved even at a high current density of 10 mA cm^-2. Besides, the decomposition of LiPF₆ is inhibited benefiting from its enhanced dissociation after the addition of DMI/LiNO₃ and DMI's function as a PF₅ scavenger. Consequently, the Li||LiFePO₄ cell succeeds to achieve an excellent capacity retention of 95.6% after 2200 cycles at a high rate of 5C, and a stable operation is realized at a high temperature of 60 °C even under harsh conditions (45 μm ultrathin Li and ∼1.5 mAh cm^-2 LiFePO₄). This work enriches the solvents and additives pool for stable and high-performance lithium metal batteries and will shed light on future developments of advanced battery electrolytes.

Optimization Strategies of Electrolytes for Low-temperature Aqueous Batteries

Aqueous rechargeable batteries (ARBs) are considered promising electrochemical energy storage systems for grid-scale applications due to their low cost, high safety, and environmental benignity. With the demand for a wide range of application scenarios, batteries are required to work in various harsh conditions, especially the cold weather. Nevertheless, electrolytes would freeze at extremely low temperatures, resulting in dramatically sluggish kinetics and severe performance degradation. Here, we discuss the behaviors of hydrogen bonds and basic principles of anti-freezing mechanisms in aqueous electrolytes. Then, we present a systematical review of the optimization strategies of electrolytes for low-temperature aqueous batteries. Finally, the challenges and promising routes for further development of aqueous low-temperature electrolytes are provided. This review can serve as a comprehensive reference to boost the further development and practical applications of advanced ARBs operated at low temperatures.

Electrochemical Proton Storage: From Fundamental Understanding to Materials to Devices

Simultaneously improving the energy density and power density of electrochemical energy storage systems is the ultimate goal of electrochemical energy storage technology. An effective strategy to achieve this goal is to take advantage of the high capacity and rapid kinetics of electrochemical proton storage to break through the power limit of batteries and the energy limit of capacitors. This article aims to review the research progress on the physicochemical properties, electrochemical performance, and reaction mechanisms of electrode materials for electrochemical proton storage. According to the different charge storage mechanisms, the surface redox, intercalation, and conversion materials are classified and introduced in detail, where the influence of crystal water and other nanostructures on the migration kinetics of protons is clarified. Several reported advanced full cell devices are summarized to promote the commercialization of electrochemical proton storage. Finally, this review provides a framework for research directions of charge storage mechanism, basic principles of material structure design, construction strategies of full cell device, and goals of practical application for electrochemical proton storage.

An Air-Rechargeable Zn/Organic Battery with Proton Storage

Air-rechargeable zinc batteries are a promising candidate for self-powered battery systems since air is ubiquitous and cost-free. However, they are still in their infancy and their electrochemical performance is unsatisfactory due to the bottlenecks of materials and device design. Therefore, it is of great significance to develop creative air-rechargeable Zn battery systems. Herein, an air-rechargeable Zn battery with H⁺-based chemistry was developed in a mild ZnSO₄ electrolyte for the first time, where benzo[i]benzo[6,7]quinoxalino[2,3-a]benzo[6,7]quinoxalino[2,3-c]phenazine-5,8,13,16,21,24-hexaone (BQPH) was employed as cathode material. In this Zn/BQPH battery, a Zn²⁺ coordination with adjacent C═O and C═N groups leads to an inhomogeneous charge distribution in the BQPH molecule, which induces the H⁺ uptake on the remaining four pairs of the C═O and C═N groups in subsequent discharge processes. Interestingly, the large potential difference between the discharged cathode of the Zn/BQPH battery and oxygen triggers the redox reaction between them spontaneously, in which the discharged cathode can be oxidized by oxygen in air. In this process, the cathode potential will gradually rise along with H⁺ removal, and the discharged Zn/BQPH battery can be air-recharged without an external power supply. As a result, the air-rechargeable Zn/BQPH batteries exhibit enhanced electrochemical performance by fast H⁺ uptake/removal. This work will broaden the horizons of air-rechargeable zinc batteries and provide a guidance to develop high-performance and sustainable aqueous self-powered systems.

Hierarchical Confinement Effect with Zincophilic and Spatial Traps Stabilized Zn-Based Aqueous Battery

Zn-based aqueous batteries (ZABs) have been regarded as promising candidates for safe and large-scale energy storage in the "post-Li" era. However, kinetics and stability problems of Zn capture cannot be concomitantly regulated, especially at high rates and loadings. Herein, a hierarchical confinement strategy is proposed to design zincophilic and spatial traps through a host of porous Co-embedded carbon cages (denoted as CoCC). The zincophilic Co sites act as preferred nucleation sites with low nucleation barriers (within 0.5 mA h cm^-2), and the carbon cage can further spatially confine Zn deposition (within 5.0 mA h cm^-2). Theoretical simulations and in situ/ex situ structural observations reveal the hierarchical spatial confinement by the elaborated all-in-one network (within 12 mA h cm^-2). Consequently, the elaborate strategy enables a dendrite-free behavior with excellent kinetics (low overpotential of ca. 65 mV at a high rate of 20 mA cm^-2) and stable cycle life (over 800 cycles), pushing forward the next-generation high-performance ZABs.

Production of a hybrid capacitive storage device via hydrogen gas and carbon electrodes coupling

Conventional electric double-layer capacitors are energy storage devices with a high specific power and extended cycle life. However, the low energy content of this class of devices acts as a stumbling block to widespread adoption in the energy storage field. To circumvent the low-energy drawback of electric double-layer capacitors, here we report the assembly and testing of a hybrid device called electrocatalytic hydrogen gas capacitor containing a hydrogen gas negative electrode and a carbon-based positive electrode. This device operates using pH-universal aqueous electrolyte solutions (i.e., from 0 to 14) in a wide temperature range (i.e., from - 70 °C to 60 °C). In particular, we report specific energy and power of 45 Wh kg^-1 and 458 W kg^-1 (both values based on the electrodes' active materials mass), respectively, at 1 A g^-1 and 25 °C with 9 M H₃PO₄ electrolyte solution. The device also enables capacitance retention of 85% (final capacitance of about 114 F g^-1) after 100,000 cycles at 10 A g^-1 and 25 °C with 1 M phosphate buffer electrolyte solution.