Rechargeable Zn-H2O hydrolysis battery for hydrogen storage and production.

Reactive metals hydrolysis offers significant advantages for hydrogen storage and production. However, the regeneration of common reactive metals (e.g., Mg, Al, etc.) is energy-intensive and produces unwanted byproducts such as CO2 and Cl2. Herein, we employ Zn as a reactive mediator that can be easily regenerated by electrolysis of ZnO in an alkaline solution with a Faradaic efficiency of >99.9 %. H2 is produced in the same electrolyte by constructing a Zn-H2O hydrolysis battery consisting of a Zn anode and a Raney-Ni cathode to unlock the Zn-H2O reaction. The entire two-step water splitting reaction with a net energy efficiency of 70.4 % at 80 °C and 50 mA cm-2. Additionally, the Zn-H2O system can be charged using renewable energy to produce H2 on demand and runs for 600 cycles only sacrificing 3.76 % energy efficiency. DFT calculations reveal that the desorption of H* on Raney-Ni (-0.30 eV) is closer to zero compared with that on Zn (-0.87 eV), indicating a faster desorption of H* at low overpotential. Further, a 24 Ah electrolyzer is demonstrated to produce H2 with a net energy efficiency of 65.5 %, which holds promise for its real application.

Balancing the Components of Biomass and the Reactivity of Pyrolysis Gas: Biomass-Assisted Recycling of Spent LiCoO2 Batteries.

Waste biomass is one of the promising feedstocks to supply syngas that can be used as fuels, chemicals, reductants, etc. However, the relationship between the component of biomass and the constituent of pyrolysis gas remains unclear. Here, we study the pyrolysis behaviors of various biomasses and reveal the relationship between the biomass components and gas compositions. Further, different pyrolysis gases are applied for the reduction of spent lithium cobalt oxide (LiCoO2) below 500 °C. The pyrolysis gas with a higher concentration of CO has a higher reductivity to convert LiCoO2 to CoO and Li2CO3 with a conversion rate close to 100% in 1 h at 500 °C. The biomass rich in cellulose and with a lower content of lignin tends to produce pyrolysis gas with a high concentration of CO, which comes from the deliberate breakdown of carboxyl, carbonyl, ether, and ester linkages. Moreover, LiCoO2 exerts catalytic functions over the deoxygenation and enhancement of oxygenates and single-ring aromatics. Overall, this paper offers a tailored approach to regulating biomass pyrolysis gases, enabling highly efficient battery recycling and syngas production.

Microzone-Acidification-Driven Degradation Mechanism of the NiFe-Based Anode in Seawater Electrolysis.

The anode stability is critical for efficient and reliable seawater electrolyzers. Herein, a NiFe-based film catalyst was prepared by anodic oxidation to serve as a model electrode, which exhibited a satisfactory oxygen evolution performance in simulated alkaline seawater (1 M KOH + 0.5 M NaCl) with an overpotential of 348 mV at 100 mA cm-2 and a long-term stability of over 100 h. After that, the effects of the current density and bulk pH of the electrolyte on its stability were evaluated. It was found that the electrode stability was sensitive to electrolysis conditions, failing at 20 mA cm-2 in 0.1 M KOH + 0.5 M NaCl but over 500 mA cm-2 in 0.5 M KOH + 0.5 M NaCl. The electrode dissolved, and some precipitates immediately formed at the region very close to the electrode surface during the electrolysis. This can be ascribed to the pH difference between the electrode/electrolyte interface and the bulk electrolyte under anodic polarization. In other words, the microzone acidification accelerates the corrosion of the electrode by Cl-, thus affecting the electrode stability. The operational performances of the electrode under different electrolysis conditions were classified to further analyze the degradation behavior, which resulted in three regions corresponding to the stable oxygen evolution, violent dissolution-precipitation, and complete passivation processes, respectively. Thereby increasing the bulk pH could alleviate the microzone acidification and improve the stability of the anode at high current densities. Overall, this study provides new insights into understanding the degradation mechanism of NiFe-based catalysts and offers electrolyte engineering strategies for the application of anodes.

Molten-Salt Electrochemical Preparation of Co2 B/MoB2 Heterostructured Nanoclusters for Boosted pH-Universal Hydrogen Evolution.

Boosting the hydrogen evolution reaction (HER) activity of α-MoB2 at large current densities and in pH-universal medium is significant for efficient hydrogen production. In this work, Co2 B/MoB2 heterostructured nanoclusters are prepared by molten-salt electrolysis (MSE) and then used as a HER catalyst. The composition, structure, and morphology of Co2 B/MoB2 can be modulated by altering the stoichiometries of raw materials and synthesis temperatures. Impressively, the obtained Co2 B/MoB2 at optimized conditions exhibits a low overpotential of 297 and 304 mV at 500 mA cm-2 in 0.5 m H2 SO4 and 1 m KOH, respectively. Moreover, the Co2 B/MoB2 catalyst possesses a long-term catalytic stability of over 190 h in both acidic and alkaline medium. The excellent HER performance is due to the modified electronic structure at the Co2 B/MoB2 heterointerface where electrons are accumulated at the Mo sites to strengthen the H adsorption. Density functional theory (DFT) calculations reveal that the formation of the Co2 B/MoB2 heterointerface decreases the H adsorption and H2 O dissociation free energies, contributing to the boosted HER intrinsic catalytic activity of Co2 B/MoB2 . Overall, this work provides an experimental and theoretical paradigm for the design of efficient pH-universal boride heterostructure electrocatalysts.

Unraveling the role of substrate materials in governing the carbon/carbide growth of molten carbonate electrolysis of CO2.

The interface interaction between deposited carbon and metallic electrode substrates in tuning the growth of CO2-derived products (e.g., amorphous carbon, graphite, carbide) is mostly unexplored for the high-temperature molten-salt electrolysis of CO2. Herein, the carbon deposition on different transition-metal cathodes was performed to reveal the role of substrate materials in the growth of cathodic products. At the initial stage of electrolysis, transition metals (e.g., Cr, Fe, Ni, and Co) that exhibit appropriate carbon-binding ability (in range of -30 to 60 kJ mol-1) allow carbon diffusing into and then dissociating from metal to form graphite, as the carbon-binding ability can be determined by the Gibbs free energy of formation of metallic carbides. The catalytic cathodes showing super strong (e.g., Ti, V, Mo, and W) or weak (e.g., Cu) carbon-binding ability produce stable carbides or amorphous carbon, respectively. However, the subsequent deposited carbon is immune to the catalysis of the substrate, forming amorphous carbon nanoparticles and nanofibers on the surface of carbides and graphite, respectively. This paper not only highlights the role of the catalytic cathodes for carbon deposition, but also offers a material selection principle for the controllable growth of CO2-derived products in molten salts.

Recovery of LiCoO2 and graphite from spent lithium-ion batteries by molten-salt electrolysis.

The recovery of spent lithium-ion batteries has not only economic value but also ecological benefits. In this paper, molten-salt electrolysis was employed to recover spent LiCoO2 batteries, in which NaCl-Na2CO3 melts were used as the electrolyte, the graphite rod and the mixtures of the spent LiCoO2 cathode and anode were used as the anode and cathode, respectively. During the electrolysis, the LiCoO2 was electrochemically reduced to Co, and Li+ and O2- entered into the molten salt. The O2- was discharged at the anode to generate CO2 and formed Li2CO3. After electrolysis, the cathodic products were separated by magnetic separation to obtain Co and graphite, and Li2CO3 was recovered by water leaching. The recovery efficiencies of Li, Co, and graphite reached 99.3%, 98.1%, and 83.6%, respectively. Overall, this paper provides a simple and efficient electrochemical method for the simultaneous recovery of the cathode and the anode of spent LiCoO2 batteries.

Improving the Initial Coulombic Efficiency of Sodium-Storage Antimony Anodes via Electrochemically Alloying Bismuth.

Improving cycling stability while maintaining a high initial Coulombic efficiency (ICE) of the antimony (Sb) anode is always a trade-off for the design of electrodes of sodium-ion batteries (SIBs). Herein, we prepare a carbon-free Sb8Bi1 anode with an ICE of 87.1% at 0.1 A g-1 by a one-step electrochemical reduction of Sb2O3 and Bi2O3 in alkaline solutions. The improved ICE of the Sb8Bi1 anode is due to the alloying of bismuth (Bi) that prevents irreversible interfacial reactions during the sodiation process. Unlike carbon buffers, the use of Bi will reduce the number of side reactions between the carbon buffer and sodium. Moreover, Bi2O3 can promote the reduction of Sb2O3 and reduce the particle size of Sb from ∼20 µm to below 300 nm. The electrolytic products can be modulated by controlling the cell voltages and electrolysis time. The electrolytic Sb8Bi1 anode delivered a capacity of 625 mAh g-1 after 200 cycles with an ICE of 87.1% at 0.1 A g-1 and even 625 mAh g-1 at 1 A g-1 over 100 cycles. Hence, alloying Bi into Sb is an effective way to make a long-lasting Sb anode while maintaining a high Coulombic efficiency.

Recovery of valuable metals from spent lithium-ion batteries through biomass pyrolysis gas-induced reduction.

The development of spent lithium-ion batteries (LIBs) recycling technologies can effectively alleviate environmental pressure and conserve metal resources. We propose a win-win strategy for pyrolysis gas reduction by lignocellulosic biomass, ensuring gas-induced reduction by spatial isolation of biomass and lithium transition metal oxides (LiTMOX (TM = Ni, Co, Mn)), and avoiding the separation of solid carbon and TMOX (TM = Ni, Co, Mn). In the spent LiCoO2 batteries, the lithium recovery efficiency reaches 99.99% and purity reaches 98.3% at 500 °C. In addition, biomass pyrolysis gas reduction is also applicable to treat spent LiMn2O4 and LiNi0.6Co0.2Mn0.2O2 batteries. Thermodynamic analysis verifies that CO dominates the gas reduction recovery process. DFT calculation indicates that the gas reduction induces the collapse of the oxygen framework of LiTMOX (TM = Ni, Co, Mn). Everbatt-based economic and environmental analysis illustrates that this is an environment-friendly and energy-saving method.

Recycling Spent Lithium-Ion Batteries Using Waste Benzene-Containing Plastics: Synergetic Thermal Reduction and Benzene Decomposition.

Spent lithium-ion batteries (LIBs) and benzene-containing polymers (BCPs) are two major pollutants that cause serious environmental burdens. Herein, spent LIBs and BCPs are copyrolyzed in a sealed reactor to generate Li2CO3, metals, and/or metal oxides without emitting toxic benzene-based gases. The use of a closed reactor allows the sufficient reduction reaction between the BCP-derived polycyclic aromatic hydrocarbon (PAH) gases and lithium transition metal oxides, achieving the Li recovery efficiencies of 98.3, 99.9, and 97.5% for LiCoO2, LiMn2O4, and LiNi0.6Co0.2Mn0.2O2, respectively. More importantly, the thermal decomposition of PAHs (e.g., phenol and benzene) is further catalyzed by the in situ generated Co, Ni, and MnO2 particles, which forms metal/carbon composites and thus prevent the emissions of toxic gases. Overall, the copyrolysis in a closed system paves a green way to synergistically recycle spent LIBs and handle waste BCPs.

An iron-base oxygen-evolution electrode for high-temperature electrolyzers.

High-temperature molten-salt electrolyzers play a central role in metals, materials and chemicals production for their merit of favorable kinetics. However, a low-cost, long-lasting, and efficient high-temperature oxygen evolution reaction (HT-OER) electrode remains a big challenge. Here we report an iron-base electrode with an in situ formed lithium ferrite scale that provides enhanced stability and catalytic activity in both high-temperature molten carbonate and chloride salts. The finding is stemmed from a discovery of the ionic potential-stability relationship and a basicity modulation principle of oxide films in molten salt. Using the iron-base electrode, we build a kiloampere-scale molten carbonate electrolyzer to efficiently convert CO2 to carbon and oxygen. More broadly, the design principles lay the foundations for exploring cheap, Earth-abundant, and long-lasting HT-OER electrodes for electrochemical devices with molten carbonate and chloride electrolytes.

New insights into engineering the core size and carbon shell thickness of Co@C core-shell catalysts for efficient and stable Fenton-like catalysis.

Herein, we engineered the cobalt core size and carbon shell thickness of Co@C by molten salt electrolysis (MSE) to investigate the enhanced essence of decreasing core size as well as the shell thickness dependence-mediated transition of catalytic mechanisms. We found that the reaction activation energy (RAE) of Co@C/peroxymonosulfate (PMS) systems was intimately dependent on the core sizes for sulfamethoxazole (SMX) degradation. The smaller core size of 26 nm provided a lower RAE of 13.39 kJ mol-1. In addition, increasing carbon shell thicknesses of Co@C altered the catalytic mechanisms from a radical pathway of SO4•- and •OH to to a non-radical pathway of 1O2 and electron-transfer process (ETP), which were verified by experimental results and density functional theory (DFT) calculations. Interestingly, increasing carbon shell thicknesses promoted the charge transfer between Co metal slab and carbon shell, increased the adsorption energy of PMS molecule on the Co@C slab, and decreased the length of OO, which favoured the occurrence of non-free radical processes.

Mechanisms of the Ammonium Sulfate Roasting of Spent Lithium-Ion Batteries.

Ammonium sulfate ((NH4)2SO4) assisted roasting has been proven to be an effective way to convert spent lithium-ion battery cathodes to water-soluble salts. Herein, thermogravimetric (TG) experiments are performed to analyze the mechanism of the sulfation conversion process. First, the reaction activation energies of the sulfate-assisted roasting are 88.87 and 95.27 kJ mol-1, which are calculated by Kissinger-Akahira-Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods, respectively. Then, nucleation and growth are determined and verified as the sulfation reaction model by the Satava-Sesták method. Finally, sub-reactions of the sulfation process are investigated and reaction controlling mechanisms are determined by the contribution of sub-reaction. Based on the thermogravimetric analysis, the phase boundary reaction is found to dominate in the initial step of the roasting process (α < 0.6) while the nucleation reaction controlls the following step (α > 0.6), agreeing well with changing trend of activation energy. Overall, thermogravimetric analysis is a general way to study the mechanism of the various roasting processes.

NaOH-assisted low-temperature roasting to recover spent LiFePO4 batteries.

Decreasing the operating temperature of pyrometallurgical methods for recycling spent lithium-ion batteries (LIBs) is key to reducing energy consumption and cost. Herein, a NaOH-assisted low-temperature roasting approach is proposed to recover spent LiFePO4. During roasting, NaOH acts as an oxidizing agent to oxidize Fe (II) to Fe3O4 at 150°C, thus collapsing its stable olivine structure while PO43- capturing Li+ and Na+ to form Li2NaPO4 and LiNa5(PO4)2. The obtained Fe3O4 is then separated, and the resulting Li salt can be further recovered as Li3PO4 with a Li recovery efficiency of 96.7 % and a purity of 99.9 %. Economic and environmental analysis based on the EverBatt model shows that this low-temperature strategy reduces energy consumption and greenhouse gas (GHG) emissions, thus increasing the potential profit. Overall, NaOH-assisted low-temperature roasting is a prospective strategy that broadens the application of NaOH as an oxidant and opens up a new avenue for decreasing the temperature of recovering spent LiFePO4 by pyrometallurgy.

Anode electrolysis of sulfides.

Traditional sulfide metallurgy produces harmful sulfur dioxide and is energy intensive. To this end, we develop an anode electrolysis approach in molten salt by which sulfide is electrochemically split into sulfur gas at a graphite inert anode while releasing metal ions that diffuse toward and are deposited at the cathode. The anodic splitting dictates the "sulfide-to-metal ion and sulfur gas" conversion that makes the reaction recur continuously. Using this approach, Cu2S is converted to sulfur gas and Cu in molten LiCl-KCl at 500 °C with a current efficiency of 99% and energy consumption of 0.420 kWh/kg-Cu (only considering the electricity for electrolysis). Besides Cu2S, the anode electrolysis can extract Cu from Cu matte that is an intermediate product from the traditional sulfide smelting process. More broadly, Fe, Ni, Pb, and Sb are extracted from FeS, CuFeS2, NiS, PbS, and Sb2S3, providing a general electrochemical method for sulfide metallurgy.

Biphase Co@C core-shell catalysts for efficient Fenton-like catalysis.

Despite the vital roles of Co nanoparticles catalytic oxidation in the Fenton-like system for eliminating pollutants, contributions of Co phases are typically overlooked. Herein, a biphase Co@C core-shell catalyst was synthesized by the electrochemical co-reduction of CaCO3 and Co3O4 in molten carbonate. Unlike the traditional pyrolysis method that is performed over 700 °C, the electrolysis was deployed at 450 °C, at which biphase structures, i.e., face-centered cubic (FCC) and hexagonal close-packed (HCP) structures, can be obtained. The biphase Co@C shows excellent catalytic oxidation performance of diethyl phthalate (DEP) with a high turnover frequency value (TOF, 28.14 min-1) and low catalyst dosage (4 mg L-1). Furthermore, density functional theory (DFT) calculations confirm that the synergistic catalytic effect of biphase Co@C is the enhancement for the breaking of the peroxide O-O bond and the charge transfer from catalysts to PMS molecule for the activation. Moreover, the results of radicals quenching experiments and electron paramagnetic resonance (EPR) tests confirm that SO4•-, •OH, O2•-, and 1O2 co-degrade DEP. Remarkably, 100% removals of three model contaminants, including DEP, sulfamethoxazole (SMX) and 2,4-dichlorophen (2,4-DCP), were achieved, either in pure water or actual river water. This paper provides an electrochemical pathway to leverage the phase of catalysts and thereby mediate their catalytic capability for remediating refractory organic contaminants.

Electrochemical Growth of High-Strength Carbon Nanocoils in Molten Carbonates.

The reported mechanical strength of carbon nanocoils (CNCs) obtained from traditional preparation of catalytic acetylene pyrolysis is far below its theoretical value. Herein, we report a molten salt electrolysis method that employs CO32- as feedstock to grow CNCs without using metal catalyst. We meticulously mediate the alkalinity of molten carbonate to tune the electrochemical reduction of CO32- on graphite electrode to selectively grow CNCs in Li2CO3-Na2CO3-K2CO3-0.001 wt %Li2O. Graphite substrate, current density, and alkalinity of molten salt dictate the growth of CNCs. In addition, the electrolytic CNCs shows a spring constant of 1.92-39.41 N/m and a shear modulus of 21-547 GPa, which are 10-200 times that of CNCs obtained from catalyst-assisted gas-to-solid conversions. Overall, this paper opens up an electrochemical way to prepare CNCs through liquid-to-solid conversion without using catalysts and acetylene, providing new perspectives on green synthesis of 1D carbon nanomaterials with high mechanical strength.

A sodium salt-assisted roasting approach followed by leaching for recovering spent LiFePO4 batteries.

Mild-temperature (<1000 °C) carbothermic reduction has been proven as an effective way to recover Li and transition metals by converting lithium transition metal oxides to transition metals/alloys and Li2CO3. However, LiFePO4 cannot be reduced by carbon because of its thermodynamically stable olivine structure. Herein, LiFePO4 is converted to Fe and lithium salts by carbon with the assistance of Na2CO3 that acts as an activating agent to break down the chemical bonds of LiFePO4 and thereby enable the carbothermic reduction. Using Na2CO3 as the activating agent, LiFePO4 was reduced to Fe, NaLi2PO4, and LiNa5(PO4)2 which can be separated by magnetic separation with a Li recovery rate of 99.2%. Using NaOH as the activating agent, LiFePO4 was oxidized to Fe3O4, NaLi2PO4 and LiNa5(PO4)2 at 600 °C, and the roasted products can be separated by magnetic separation process with a Li recovery rate of 92.7%. Various sodium salts were tested to screen proper salts for the reduction process, and a 400-g scale roasting-separation process has been demonstrated. Overall, the salt-assisted roasting is a promising way to recycle spent LiFePO4 batteries without using strong mineral acids and shows great potential for the industrial-scale implementation.

Effect of a Magnetic Field on the Electrode Process of Al Electrodeposition in a [Emim]Cl-AlCl3 Ionic Liquid.

The magnetohydrodynamic (MHD) effect was usually used to improve the mass transport during electrodeposition in a solution electrolyte. Herein, we reported the effect of a magnetic field on the electrode process of Al electrodeposition in a [Emim]Cl-AlCl3 ionic liquid composed of pure ions. Under a uniform and perpendicular magnetic field to the Cu electrode plane, electrochemical impedance spectroscopy (EIS) of the circuit, the cyclic voltammetry (CV) curves, and the different capacitances at the potential of zero charge (PZC) were measured, and the electrodeposition of aluminum was carried out at a constant current density. The results indicated that a vertical magnetic field significantly reduced the resistance (activation energy) for charge transfer of electrochemical reduction of Al2Cl7-; meanwhile, the capacitance of an electric double layer (EDL) and the density of the electrodeposited aluminum layer were increased.

A durable and pH-universal self-standing MoC-Mo2C heterojunction electrode for efficient hydrogen evolution reaction.

Efficient water electrolyzers are constrained by the lack of low-cost and earth-abundant hydrogen evolution reaction (HER) catalysts that can operate at industry-level conditions and be prepared with a facile process. Here we report a self-standing MoC-Mo2C catalytic electrode prepared via a one-step electro-carbiding approach using CO2 as the feedstock. The outstanding HER performances of the MoC-Mo2C electrode with low overpotentials at 500 mA cm-2 in both acidic (256 mV) and alkaline electrolytes (292 mV), long-lasting lifetime of over 2400 h (100 d), and high-temperature performance (70 oC) are due to the self-standing hydrophilic porous surface, intrinsic mechanical strength and self-grown MoC (001)-Mo2C (101) heterojunctions that have a ΔGH* value of -0.13 eV in acidic condition, and the energy barrier of 1.15 eV for water dissociation in alkaline solution. The preparation of a large electrode (3 cm × 11.5 cm) demonstrates the possibility of scaling up this process to prepare various carbide electrodes with rationally designed structures, tunable compositions, and favorable properties.