CO Intermediate-Assisted Dynamic Cu Sintering During Electrocatalytic CO2 Reduction on Cu-N-C Catalysts.

The electrochemical CO2 reduction reaction (eCO2RR) to multicarbon products has been widely recognized for Cu-based catalysts. However, the structural changes in Cu-based catalysts during the eCO2RR pose challenges to achieving an in-depth understanding of the structure-activity relationship, thereby limiting catalyst development. Herein, we employ constant-potential density functional theory calculations to investigate the sintering process of Cu single atoms of Cu-N-C single-atom catalysts into clusters under eCO2RR conditions. Systematic constant-potential ab initio molecular dynamics simulations revealed that the leaching of Cu-(CO)x moieties and subsequent agglomeration into clusters can be facilitated by synergistic adsorption of H and eCO2RR intermediates (e.g., CO). Increasing the Cu2+ concentration or the applied potential can efficiently suppress Cu sintering. Both microkinetic simulations and experimental results further confirm that sintered Cu clusters play a crucial role in generating C2 products. These findings provide significant insights into the dynamic evolution of Cu-based catalysts and the origin of their activity toward C2 products during the eCO2RR.

Artificial LiF-Rich Interface Enabled by In situ Electrochemical Fluorination for Stable Lithium-Metal Batteries.

Lithium (Li)-metal batteries are promising next-generation energy storage systems. One drawback of uncontrollable electrolyte degradation is the ability to form a fragile and nonuniform solid electrolyte interface (SEI). In this study, we propose the use of a fluorinated carbon nanotube (CNT) macrofilm (CMF) on Li metal as a hybrid anode, which can regulate the redox state at the anode/electrolyte interface. Due to the favorable reaction energy between the plated Li and fluorinated CNTs, the metal can be fluorinated directly to a LiF-rich SEI during the charging process, leading to a high Young's modulus (~2.0 GPa) and fast ionic transfer (~2.59×10-7  S cm-1 ). The obtained SEI can guide the homogeneous plating/stripping of Li during electrochemical processes while suppressing dendrite growth. In particular, the hybrid of endowed full cells with substantially enhanced cyclability allows for high capacity retention (~99.3 %) and remarkable rate capacity. This work can extend fluorination technology into a platform to control artificial SEI formation in Li-metal batteries, increasing the stability and long-term performance of the resulting material.

Durable CO2 conversion in the proton-exchange membrane system.

Electrolysis that reduces carbon dioxide (CO2) to useful chemicals can, in principle, contribute to a more sustainable and carbon-neutral future1-6. However, it remains challenging to develop this into a robust process because efficient conversion typically requires alkaline conditions in which CO2 precipitates as carbonate, and this limits carbon utilization and the stability of the system7-12. Strategies such as physical washing, pulsed operation and the use of dipolar membranes can partially alleviate these problems but do not fully resolve them11,13-15. CO2 electrolysis in acid electrolyte, where carbonate does not form, has therefore been explored as an ultimately more workable solution16-18. Herein we develop a proton-exchange membrane system that reduces CO2 to formic acid at a catalyst that is derived from waste lead-acid batteries and in which a lattice carbon activation mechanism contributes. When coupling CO2 reduction with hydrogen oxidation, formic acid is produced with over 93% Faradaic efficiency. The system is compatible with start-up/shut-down processes, achieves nearly 91% single-pass conversion efficiency for CO2 at a current density of 600 mA cm-2 and cell voltage of 2.2 V and is shown to operate continuously for more than 5,200 h. We expect that this exceptional performance, enabled by the use of a robust and efficient catalyst, stable three-phase interface and durable membrane, will help advance the development of carbon-neutral technologies.

Boosted Oxygen Kinetics of Hierarchically Mesoporous Mo2C/C for High-current-density Zn-air Battery.

The high-current-density Zn-air battery shows big prospects in next-generation energy technologies, while sluggish O2 reaction and diffusion kinetics barricade the applications. Herein, the sequential assembly is innovatively demonstrated for hierarchically mesoporous molybdenum carbides/carbon microspheres with a tunable thickness of mesoporous carbon layers (Meso-Mo2C/C-x, where x represents the thickness). The optimum Meso-Mo2C/C-14 composites (≈2 µm in diameter) are composed of mesoporous nanosheets (≈38 nm in thickness), which possess bilateral mesoporous carbon layers (≈14 nm in thickness), inner Mo2C/C layers (≈8 nm in thickness) with orthorhombic Mo2C nanoparticles (≈2 nm in diameter), a high surface area of ≈426 m2 g-1, and open mesopores (≈6.9 nm in size). Experiments and calculations corroborate the hierarchically mesoporous Mo2C/C can enhance hydrophilicity for supplying sufficient O2, accelerate oxygen reduction kinetics by highly-active Mo2C and N-doped carbon sites, and facilitate O2 diffusion kinetics over hierarchically mesopores. Therefore, Meso-Mo2C/C-14 outputs a high half-wave potential (0.88 V vs RHE) with a low Tafel slope (51 mV dec-1) for oxygen reduction. More significantly, the Zn-air battery delivers an ultrahigh power density (272 mW cm-2), and an unprecedented 100 h stability at a high-current-density condition (100 mA cm-2), which is one of the best performances.

Advanced Catalyst Design and Reactor Configuration Upgrade in Electrochemical Carbon Dioxide Conversion.

Electrochemical carbon dioxide reduction reaction (CO2 RR) driven by renewable energy shows great promise in mitigating and potentially reversing the devastating effects of anthropogenic climate change and environmental degradation. The simultaneous synthesis of energy-dense chemicals can meet global energy demand while decoupling emissions from economic growth. However, the development of CO2 RR technology faces challenges in catalyst discovery and device optimization that hinder their industrial implementation. In this contribution, a comprehensive overview of the current state of CO2 RR research is provided, starting with the background and motivation for this technology, followed by the fundamentals and evaluated metrics. Then the underlying design principles of electrocatalysts are discussed, emphasizing their structure-performance correlations and advanced electrochemical assembly cells that can increase CO2 RR selectivity and throughput. Finally, the review looks to the future and identifies opportunities for innovation in mechanism discovery, material screening strategies, and device assemblies to move toward a carbon-neutral society.

Regulated High-Spin State and Constrained Charge Behavior of Active Cobalt Sites in Covalent Organic Frameworks for Promoting Electrocatalytic Oxygen Reduction.

A novel type of covalent organic frameworks has been developed by assembling definite cobalt-nitrogen-carbon configurations onto carbon nanotubes using linkers that have varying electronic effects. This innovative approach has resulted in an efficient electrocatalyst for oxygen reduction, which is understood by a combination of in situ spectroelectrochemistry and the bond order theorem. The strong interaction between the electron-donating carbon nanotubes and the electron-accepting linker mitigates the trend of charge loss at cobalt sites, while inducing the generation of high spin state. This enhances the adsorption strength and electron transfer between the cobalt center and reactants/intermediates, leading to an improved oxygen reduction capability. This work not only presents an effective strategy for developing efficient non-noble metal electrocatalysts through reticular chemistry, but also provides valuable insights into regulating the electronic configuration and charge behavior of active sites in designing high-performance electrocatalysts.

Regulating Reversible Oxygen Electrocatalysis by Built-in Electric Field of Heterojunction Electrocatalyst with Modified d-Band.

Developing bifunctional catalysts for oxygen electrochemical reactions is essential for high-performance electrochemical energy devices. Here, a Mott-Schottky heterojunction composed of porous cobalt-nitrogen-carbon (Co-N-C) polyhedra containing abundant metal-phosphides for reversible oxygen electrocatalysis is reported. As a demonstration, this catalyst shows excellent activity in the oxygen electrocatalysis and thus delivers outstanding performance in rechargeable zinc-air batteries (ZABs). The built-in electric field in the Mott-Schottky heterojunction can promote electron transfer in oxygen electrocatalysis. More importantly, an appropriate d-band center of the heterojunction catalyst also endows oxygen intermediates with a balanced adsorption/desorption capability, thus enhancing oxygen electrocatalysis and consequently improving the performance of ZABs. The work demonstrates an important design principle for preparing efficient multifunctional catalysts in energy conversion technologies.

An integrated platinum-nanocarbon electrocatalyst for efficient oxygen reduction.

Efficient and robust platinum-carbon electrocatalysts are of great significance for the long-term service of high-performance fuel cells. Here, we report a Pt alloy integrated in a cobalt-nitrogen-nanocarbon matrix by a multiscale design principle for efficient oxygen reduction reaction. This Pt integrated catalyst demonstrates an increased mass activity, 11.7 times higher than that of commercial Pt catalyst, and retains a stability of 98.7% after 30,000 potential cycles. Additionally, this integrated catalyst delivers a current density of 1.50 A cm-2 at 0.6 V in the hydrogen-air fuel cell and achieves a power density of 980 mW cm-2. Comprehensive investigations demonstrate that the synergistic contribution of components and structure in the platinum-carbon integrated catalyst is responsible for the high-efficiency ORR in fuel cells.

Dual-Network Structured Hydrogel Electrolytes Engaged Solid-State Rechargeable Zn-Air/Iodide Hybrid Batteries.

As a key component of batteries, the electrolyte determines the ion transport and interface chemistry of the cathode and anode. In this work, we develop a dual-network structured hydrogel electrolyte composed of polyacrylamide (PAM), sodium alginate (SA) and potassium iodide (KI) for solid-state zinc-air/iodide hybrid batteries. The assembled hybrid battery shows excellent renewability and a long cycling life of 110 h with a high energy efficiency of 80 %. The ion-crosslinked dual-network structure endows the material with improved mechanical strength and increased ionic conductivity. More importantly, the introduction of iodine species not only offers more favorable cathodic kinetics of iodide/iodate redox than oxygen electrocatalysis but also regulates the solvation structure of zinc ions to ensure better interface stability. This work provides significant concepts for developing novel solid-state electrolytes to realize high-performance energy devices and technologies.

Carbon-Confined Indium Oxides for Efficient Carbon Dioxide Reduction in a Solid-State Electrolyte Flow Cell.

Developing robust electrocatalysts and advanced devices is important for electrochemical carbon dioxide (CO2 ) reduction toward the generation of valuable chemicals. We present herein a carbon-confined indium oxide electrocatalyst for stable and efficient CO2 reduction. The reductive corrosion of oxidative indium to the metallic state during electrolysis could be prevented by carbon protection, and the applied carbon layer also optimizes the reaction intermediate adsorption, which enables both high selectivity and activity for CO2 reduction. In a liquid-phase flow cell, the formate selectivity exceeds 90 % in a wide potential window from -0.8 V to -1.3 V vs. RHE. The continuous production of ca. 0.12 M pure formic acid solution is further demonstrated at a current density of 30 mA cm-2 in a solid-state electrolyte mediated reactor. This work provides significant concepts in the parallel development of electrocatalysts and devices for carbon-neutral technologies.

A Substrate-Induced Fabrication of Active Free-Standing Nanocarbon Film as Air Cathode in Rechargeable Zinc-Air Batteries.

Designing cost-effective and high-efficiency bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) occurred at air electrodes is vitally significant yet challenging for Zn-air batteries (ZABs). In this work, a zinc substrate induced fabrication is reported of free-standing nanocarbon hybrid film which shows good bifunctional activity and can be directly used as the air electrode in the rechargeable ZABs. The designed nanocarbon film in Zn-air battery provides a satisfactory power density of 185 mW cm-2 and cycling stability for 1200 h under the current density of 10 mA cm-2 . This hybrid film also gives a solid-state ZAB excellent flexibility with a power density of 160 mW cm-2 . The free-standing hybrid with abundant cobalt-nitrogen-carbon species coupled with porous architecture would be the original factor for its satisfactory performance of rechargeable ZABs. This work would pave an ideal way to design integrated electrode with high electrocatalytic performance towards electrochemical energy technologies.

Recent Advances on MOF Derivatives for Non-Noble Metal Oxygen Electrocatalysts in Zinc-Air Batteries.

Oxygen electrocatalysts are of great importance for the air electrode in zinc-air batteries (ZABs). Owing to the high specific surface area, controllable pore size and unsaturated metal active sites, metal-organic frameworks (MOFs) derivatives have been widely studied as oxygen electrocatalysts in ZABs. To date, many strategies have been developed to generate efficient oxygen electrocatalysts from MOFs for improving the performance of ZABs. In this review, the latest progress of the MOF-derived non-noble metal-oxygen electrocatalysts in ZABs is reviewed. The performance of these MOF-derived catalysts toward oxygen reduction, and oxygen evolution reactions is discussed based on the categories of metal-free carbon materials, single-atom catalysts, metal cluster/carbon composites and metal compound/carbon composites. Moreover, we provide a comprehensive overview on the design strategies of various MOF-derived non-noble metal-oxygen electrocatalysts and their structure-performance relationship. Finally, the challenges and perspectives are provided for further advancing the MOF-derived oxygen electrocatalysts in ZABs.

A Zeolitic-Imidazole Framework-Derived Trifunctional Electrocatalyst for Hydrazine Fuel Cells.

Hydrazine fuel cells are promising sustainable power sources. However, the high price and limited reserves of noble metal catalysts that promote the sluggish cathodic and anodic electrochemical reactions hinder their practical applications. Reflecting the enhanced diffusion and improved kinetics of nanostructured non-noble metal electrocatalysts, we report an efficient zeolitic-imidazole framework-derived trifunctional electrocatalyst for hydrazine oxidation, oxygen, and hydrogen peroxide reduction. Experimental results and theoretical calculations corroborate that the nanocarbon architecture with abundant Co-N species enhances the electronic interaction and optimizes the energy barriers of anodic hydrazine oxidation and cathodic oxygen reduction. The resulting assembled hydrazine-oxygen fuel cell yields a cell voltage and power density of 0.74 V and 20.5 mW cm-2, respectively. Moreover, benefiting from the liquid-liquid diffusion, the hydrazine-hydrogen peroxide cell shows a boosted cell voltage and power density, corresponding to 1.68 V and 41.0 mW cm-2. This work offers a highly active non-noble metal multifunctional electrocatalyst with a pioneering diffusion philosophy in the liquid electrochemical cells.

Efficient Electroconversion of Carbon Dioxide to Formate by a Reconstructed Amino-Functionalized Indium-Organic Framework Electrocatalyst.

We report an amino-functionalized indium-organic framework for efficient CO2 reduction to formate. The immobilized amino groups strengthen the absorption and activation of CO2 and stabilize the active intermediates, which endow an enhanced catalytic conversion to formate despite the inevitable reduction and reconstruction of the functionalized indium-based catalyst during electrocatalysis. The reconstructed amino-functionalized indium-based catalyst demonstrates a high Faradaic efficiency of 94.4 % and a partial current density of 108 mA cm-2 at -1.1 V vs. RHE in a liquid-phase flow cell, and also delivers an enhanced current density of ca. 800 mA cm-2 at 3.4 V for the formate production in a gas-phase flow cell configuration. This work not only provides a molecular functionalization and assembling concept of hybrid electrocatalysts but also offers valuable understandings in electrocatalyst evolution and reactor optimization for CO2 electrocatalysis and beyond.