Metal–Organic Layers Leading to Atomically Thin Bismuthene for Efficient Carbon Dioxide Electroreduction to Liquid Fuel

Hetero-Anionic Structure Activated CoS Bonds Promote Oxygen Electrocatalytic Activity for High-Efficiency Zinc-Air Batteries

The electronic structure of transition metal complexes can be modulated by replacing partial ion of complexes to obtain tuned intrinsic oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) electrocatalytic activity. However, the anion-modulated transition metal complexes ORR activity of is still unsatisfactory, and the construction of hetero-anionic structure remains challenging. Herein, an atomic doping strategy is presented to prepare the CuCo2 O4-x Sx /NC-2 (CCSO/NC-2) as electrocatalysts, the structrual characterization results favorably demonstrate the partial substitution of S atoms for O in CCSO/NC-2, which shows excellent catalytic performance and durability for OER and ORR in 0.1 m KOH. In addition, the catalyst assembled Zinc-air battery with an open circuit potential of 1.43 V maintains performance after 300 h of cyclic stability. Theoretical calculations and differential charges illustrate that S doping optimizes the reaction kinetics and promotes electron redistribution. The superior performance of CCSO/NC-2 catalysis is mainly due to its unique S modulation of the electronic structure of the main body. The introduction of S promotes CoO covalency and constructs a fast electron transport channel, thus optimizing the adsorption degree of active site Co to the reaction intermediates.

Halogen-Incorporated Sn Catalysts for Selective Electrochemical CO2 Reduction to Formate

Electrochemically reducing CO₂ to valuable fuels or feedstocks is recognized as a promising strategy to simultaneously tackle the crises of fossil fuel shortage and carbon emission. Sn-based catalysts have been widely studied for electrochemical CO₂ reduction reaction (CO₂ RR) to make formic acid/formate, which unfortunately still suffer from low activity, selectivity and stability. In this work, halogen (F, Cl, Br or I) was introduced into the Sn catalyst by a facile hydrolysis method. The presence of halogen was confirmed by a collection of ex situ and in situ characterizations, which rendered a more positive valence state of Sn in halogen-incorporated Sn catalyst as compared to unmodified Sn under cathodic potentials in CO₂ RR and therefore tuned the adsorption strength of the key intermediate (*OCHO) toward formate formation. As a result, the halogen-incorporated Sn catalyst exhibited greatly enhanced catalytic performance in electrochemical CO₂ RR to produce formate.

Interface Engineering on Amorphous/Crystalline Hydroxides/Sulfides Heterostructure Nanoarrays for Enhanced Solar Water Splitting

Developing highly efficient and stable noble-metal-free electrocatalysts for water splitting is critical for producing clean and sustainable energy. Here, we design a hierarchical transition metal hydroxide/sulfide (NiFe(OH)_x-Ni₃S₂/NF) electrode with dual heterointerface coexistence using a cation exchange-induced surface reconfiguration strategy. The electrode exhibits superior electrocatalytic activities, achieving low overpotentials of 55 mV for hydrogen evolution and 182 mV for oxygen evolution at 10 mA cm^-2. Furthermore, the assembled two-electrode system requires voltages as low as 1.55 and 1.62 V to deliver industrially relevant current densities of 500 and 1000 mA cm^-2, respectively, with excellent durability for over 200 h, which is comparable to commercial electrolysis. Theoretical calculations reveal that the hierarchical heterostructure increases the electronic delocalization of the Fe and Ni catalytic centers, lowering the energy barrier of the rate-limiting step and promoting O₂ desorption. Finally, by implementing the catalysts in a solar-driven water electrolysis system, we demonstrate a record and durable solar-to-hydrogen (STH) conversion efficiency of up to 20.05%. This work provides a promising strategy for developing low-cost and high-efficiency bifunctional catalysts for a large-scale solar-to-hydrogen generation.

Alloying Co Species into Ordered and Interconnected Macroporous Carbon Polyhedra for Efficient Oxygen Reduction Reaction in Rechargeable Zinc-Air Batteries

Engineering non-precious transition metal (TM)-based electrocatalysts to simultaneously achieve an optimal intrinsic activity, high density of active sites, and rapid mass transfer ability for the oxygen reduction reaction (ORR) remains a significant challenge. To address this challenge, a hybrid composite consisting of Fe_x Co alloy nanoparticles uniformly implanted into hierarchically ordered macro-/meso-/microporous N-doped carbon polyhedra (HOMNCP) is rationally designed. The combined results of experimental and theoretical investigations indicate that the alloying of Co enables a favorable electronic structure for the formation of the *OH intermediate, while the periodically trimodal-porous structured carbon matrix structure not only provides highly accessible channels for active site utilization but also dramatically facilitates mass transfer in the catalytic process. As expected, the Fe_0.5 Co@HOMNCP composite catalyst exhibits extraordinary ORR activity with a half-wave potential of 0.903 V (vs reversible hydrogen electrode), surpassing most Co-based catalysts reported to date. More remarkably, the use of the Fe_0.5 Co@HOMNCP catalyst as the air electrode in a zinc-air battery results in superior open-circuit voltage and power density compared to a commercial Pt/C + IrO₂ catalyst. The results of this study are expected to inspire the development of advanced TM-based catalysts for energy storage and conversion applications.

Efficient and Selective CO2 Reduction to Formate on Pd-Doped Pb3 (CO3 )2 (OH)2 : Dynamic Catalyst Reconstruction and Accelerated CO2 Protonation

Exploring catalyst reconstruction under the electrochemical condition is critical to understanding the catalyst structure-activity relationship as well as to design effective electrocatalysts. Herein, a PbF₂ nanocluster is synthesized and its self-reconstruction under the CO₂ reduction condition is investigated. F^- leaching, CO₂ -saturated environment, and application of a cathodic potential induce self-reconstruction of PbF₂ to Pb₃ (CO₃ )₂ (OH)₂ , which effectively catalyze the CO₂ reduction to formate. The in situ formed Pb₃ (CO₃ )₂ (OH)₂ discloses >80% formate Faradaic efficiencies (FEs) across a broad range of potentials and achieves a maximum formate FE of ≈90.1% at -1.2 V versus reversible hydrogen electrode (RHE). Kinetic studies show that the CO₂ reduction reaction (CO₂ RR) on the Pb₃ (CO₃ )₂ (OH)₂ is rate-limited at the CO₂ protonation step, in which proton is supplied by bicarbonate (HCO₃ ^- ) in the electrolyte. To improve the CO₂ RR kinetics, the Pb₃ (CO₃ )₂ (OH)₂ is further doped with Pd (4 wt%) to enhance its HCO₃ ^- adsorption, which leads to accelerated protonation of CO₂ . Therefore, the Pd-Pb₃ (CO₃ )₂ (OH)₂ (4 wt%) reveals higher formate FEs of >90% from -0.8 to -1.2 V versus RHE and reaches a maximum formate FE of 96.5% at -1.2 V versus RHE with a current density of ≈13 mA cm^-2 .

Anchoring Ionic Liquid in Copper Electrocatalyst for Improving CO2 Conversion to Ethylene

Electrochemical conversion of CO₂ to valuable fuels is appealing for CO₂ fixation and energy storage. The Cu-based catalysts feature unique superiorities, but achieving high ethylene selectivity is still restricted. In this study, we propose the anchoring of an ionic liquid (IL) on a Cu electrocatalyst for improving the electrochemical CO₂ reduction to ethylene. In a water-based electrolyte and a commonly used H-type cell, a high ethylene Faradaic efficiency of 77.3 % was achieved at -1.49 V (vs. RHE). Experimental and theoretical studies reveal that an IL can modify the electronic structure of a Cu catalyst through its interaction with Cu, making it more conducive to *CO dimerization for ethylene formation.

Porphyrin-Based COF 2D Materials: Variable Modification of Sensing Performances by Post-Metallization

2D nanomaterials with flexibly modifiable surfaces are highly sought after for various applications, especially in room-temperature chemiresistive gas sensing. Here, we have prepared a series of COF 2D nanomaterials (porphyrin-based COF nanosheets (NS)) that enabled highly sensitive and specific-sensing of NO₂ at room temperature. Different from the traditional 2D sensing materials, H₂ -TPCOF was designed with a largely reduced interlayer interaction and predesigned porphyrin rings as modifiable sites on its surfaces for post-metallization. After post-metallization, the metallized M-TPCOF (M=Co and Cu) showed remarkably improved sensing performances. Among them, Co-TPCOF exhibited highly specific sensing toward NO₂ with one of the highest sensitivities of all reported 2D materials and COF materials, with an ultra-low limit-of-detection of 6.8 ppb and fast response/recovery. This work might shed light on designing and preparing a new type of surface-highly-modifiable 2D material for various chemistry applications.

Maximizing Electroactive Sites in a Three-Dimensional Covalent Organic Framework for Significantly Improved Carbon Dioxide Reduction Electrocatalysis

Synthesis of functional 3D COFs with irreversible bond is challenging. Herein, 3D imide-bonded COFs were constructed via the imidization reaction between phthalocyanine-based tetraanhydride and 1,3,5,7-tetra(4-aminophenyl)adamantine. These two 3D COFs are made up of interpenetrated pts networks according to powder X-ray diffraction and gas adsorption analyses. CoPc-PI-COF-3 doped with carbon black has been employed to fabricate the electrocatalytic cathode towards CO₂ reduction reaction within KHCO₃ aqueous solution, displaying the Faradaic efficiency of 88-96 % for the CO₂ -to-CO conversion at the voltage range of ca. -0.60 to -1.00 V (vs. RHE). In particular, the 3D porous structure of CoPc-PI-COF-3 enables the active electrocatalytic centers occupying 32.7 % of total cobalt-phthalocyanine subunits, thus giving a large current density (j_CO ) of -31.7 mA cm^-2 at -0.90 V. These two parameters are significantly improved than the excellent 2D COF analogue (CoPc-PI-COF-1, 5.1 % and -21.2 mA cm^-2 ).

ZnO-Co3O4/N-C Cage Derived from the Hollow Zn/Co ZIF for Enhanced Degradation of Bisphenol A with Persulfate

The zeolitic imidazolate framework (ZIF)-67 microcrystal was employed as a precursor to synthesize the hollow ZIF-8/ZIF-67 composite via the epitaxial growth of ZIF-8 on ZIF-67, in situ self-sacrifice, and excavation of ZIF-67. The hollow ZIF-8/ZIF-67 composite was successfully transformed to the ZnO-Co₃O₄/N-C cage by thermal treatment, which was further used as the catalyst for the oxidative degradation of bisphenol A (BPA) in the presence of potassium persulfate (PS). In comparison with the Co₃O₄/N-C and Co₃O₄ obtained from pure ZIF-67 and cobalt nitrate, the ZnO-Co₃O₄/N-C cage demonstrated a more than four fold-higher activity and robust reusability. Based on structural analysis, the enhanced catalytic performance could be ascribed to the small, highly dispersed cobalt oxide particles, the hollow structure that facilitated the transportation of the molecules, and the synergistic effect between cobalt oxide and nitrogen-doped carbon in the composite. Besides, the effect of dosage of PS, BPA, and the co-existing components such as chloride ion, methanol, and t-butyl alcohol was carefully investigated to propose the possible mechanism. This study would give new insights into the design of functional composite materials from metal organic frameworks and the development of their application in environmental pollution disposal.

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.

The Controllable Reconstruction of Bi-MOFs for Electrochemical CO2 Reduction through Electrolyte and Potential Mediation

Monitoring and controlling the reconstruction of materials under working conditions is crucial for the precise identification of active sites, elucidation of reaction mechanisms, and rational design of advanced catalysts. Herein, a Bi-based metal-organic framework (Bi-MOF) for electrochemical CO₂ reduction is selected as a case study. In situ Raman spectra combined with ex situ electron microscopy reveal that the intricate reconstruction of the Bi-MOF can be controlled using two steps: 1) electrolyte-mediated dissociation and conversion of Bi-MOF to Bi₂ O₂ CO₃ , and 2) potential-mediated reduction of Bi₂ O₂ CO₃ to Bi. The intentionally reconstructed Bi catalyst exhibits excellent activity, selectivity, and durability for formate production, and the unsaturated surface Bi atoms formed during reconstruction become the active sites. This work emphasizes the significant impact of pre-catalyst reconstruction under working conditions and provides insight into the design of highly active and stable electrocatalysts through the regulation of these processes.

Boron Dopant Induced Electron-Rich Bismuth for Electrochemical CO2 Reduction with High Solar Energy Conversion Efficiency

Electrochemical CO₂ reduction to formate offers a mild and feasible pathway for the utilization of CO₂ , and bismuth is a promising metal for its unique hydrogen evolution reaction inhibition. Reported works of Bi-based electrodes generally exhibit high selectivity while suffering from relatively narrow working potential range. From the perspective of electronic modification engineering, B-doped Bi is prepared by a facile chemical reduction method in this work. With B dopant, above 90% Faradaic efficiency for formate over a broad window of working potential of -0.6 to -1.2 V (vs. reversible hydrogen electrode) is achieved. In situ Raman spectroscopy, X-ray adsorption spectroscopy, and computational analysis demonstrate that the B dopant induces the formation of electron-rich bismuth, which is in favor of the formation of formate by fine-tuning the adsorption energy of *OCHO. Moreover, full-cell electrolysis system coupled with photovoltaic device is constructed and achieves the solar-to-formate conversion efficiency as high as 11.8%.

A general strategy for obtaining BiOX nanoplates derived Bi nanosheets as efficient CO2 reduction catalysts by enhancing CO2•- adsorption and electron transfer

Electroreduction of carbon dioxide (CO₂) into formic acid/formate has been considered as one of the most promising strategies for obtaining value-added fuels and chemical productions. Herein, we present a general method for preparing Bi-based electrocatalysts via in situ reduction of bismuth oxyiodide (BiOI) in CO₂-saturated electrolyte. The precursors of BiOI nanoplates (P-nanoplates) with thickness of 30-40 nm could be easily obtained and provide a concise model to probe the mechanisms of CO₂ reduction to formate. BiOI nanoplates precursors derived Bi nanosheets (P-nanoplates-Bi) exhibited an excellent performance for CO₂ reduction to formate, achieving Faradaic efficiencies (FEs) over 80% in a wide potential window and a maximum FE approaching of 95% with a current density of 13.3 ± 0.6 mA cm^-2 at -0.9 V versus reverse hydrogen electrode (υs. RHE). Such P-nanoplates-Bi nanosheets showed a stable electrocatalytic actitivity during 15 h operation in 0.5 M KHCO₃ aqueous solution. The superior performance is mainly attributed to the two-dimensional (2D) Bi nanosheets, which can increase CO₂^•- adsorption, enlarge active surface area, show better reaction kinetics and provide lower contact resistance with accelerated electron transfer. For comparison, precursors of BiOI plate-like (P-bulk) with doubled thicknesses and ultrathin BiOI with a few nanometers derived Bi catalysts tend to agglomerate and appear as irregular structured Bi nanoparticles during the reaction. Their peak FEs for formate are much lower than those of P-nanoplates derived Bi nanosheets at -0.9 V.

MOFs-Derived Carbon-Based Metal Catalysts for Energy-Related Electrocatalysis

Electrochemical devices, as renewable and clean energy systems, display a great potential to meet the sustainable development in the future. However, well-designed and highly efficient electrocatalysts are the technological dilemmas that retard their practical applications. Metal-organic frameworks (MOFs) derived electrocatalysts exhibit tunable structure and intriguing activity and have received intensive investigation in recent years. In this review, the recent progress of MOFs-derived carbon-based single atoms (SAs) and metal nanoparticles (NPs) catalysts for energy-related electrocatalysis is summarized. The effects of synthesis strategy, coordination environment, morphology, and composition on the catalytic activity are highlighted. Furthermore, these SAs and metal NPs catalysts for the applications of electrocatalysis (hydrogen evolution reaction, oxygen evolution reaction, oxygen reduction reaction, carbon dioxide reduction reaction, and nitrogen reduction reaction) are overviewed. Finally, some current challenges and foresighted ideas for MOFs-derived carbon-based metal electrocatalysts are presented.

Engineering Bismuth-Tin Interface in Bimetallic Aerogel with a 3D Porous Structure for Highly Selective Electrocatalytic CO2 Reduction to HCOOH

Electrochemical reduction of CO₂ (CO₂ RR) into valuable hydrocarbons is appealing in alleviating the excessive CO₂ level. We present the very first utilization of metallic bismuth-tin (Bi-Sn) aerogel for CO₂ RR with selective HCOOH production. A non-precious bimetallic aerogel of Bi-Sn is readily prepared at ambient temperature, which exhibits 3D morphology with interconnected channels, abundant interfaces and a hydrophilic surface. Superior to Bi and Sn, the Bi-Sn aerogel exposes more active sites and it has favorable mass transfer properties, which endow it with a high FE_HCOOH of 93.9 %. Moreover, the Bi-Sn aerogel achieves a FE_HCOOH of ca. 90 % that was maintained for 10 h in a flow battery. In situ ATR-FTIR measurements confirmed that the formation of *HCOO is the rate-determining step toward formic acid generation. DFT demonstrated the coexistence of Bi and Sn optimized the energy barrier for the production of HCOOH, thereby improving the catalytic activity.

In Situ Bismuth Nanosheet Assembly for Highly Selective Electrocatalytic CO2 Reduction to Formate

The reduction of carbon dioxide (CO₂ ) into value-added fuels using an electrochemical method has been regarded as a compelling sustainable energy conversion technology. However, high-performance electrocatalysts for CO₂ reduction reaction (CO₂ RR) with high formate selectivity and good stability need to be improved. Earth-abundant Bi has been demonstrated to be active for CO₂ RR to formate. Herein, we fabricated an extremely active and selective bismuth nanosheet (Bi-NSs) assembly via an in situ electrochemical transformation of (BiO)₂ CO₃ nanostructures. The as-prepared material exhibits high activity and selectivity for CO₂ RR to formate, with nearly 94% faradaic efficiency at -1.03 V (versus reversible hydrogen electrode (vs. RHE)) and stable selectivity (>90%) in a large potential window ranging from -0.83 to -1.18 V (vs. RHE) and excellent durability during 12 h continuous electrolysis. In addition, the Bi-NSs based CO₂ RR/methanol oxidation reaction (CO₂ RR/MOR) electrolytic system for overall CO₂ splitting was constructed, evidencing the feasibility of its practical implementation.

Hydrangea-like Superstructured Micro/Nanoreactor of Topotactically Converted Ultrathin Bismuth Nanosheets for Highly Active CO2 Electroreduction to Formate

An electrocatalytic carbon dioxide reduction reaction (CO₂RR) is an appealing route to obtain the value-added feedstocks and alleviate the energy crisis. However, how to achieve high-performance electrocatalysts for CO₂ reduction to formate is challenging owing to the poor intrinsic activity, insufficient conductivity, and low surface density of active sites. Herein, we fabricated an extremely active and selective hydrangea-like superstructured micro/nanoreactor of ultrathin bismuth nanosheets through an in situ electrochemical topotactic transformation of hierarchical bismuth oxide formate (BiOCOOH). The resulted bismuth nanosheet superstructure is in the form of three-dimensional intercrossed networks of ultrathin nanosheets, forming an ordered open porous structure through self-assembly, which can be used as a micro/nanoreactor to enable a large electrochemically active surface area as well as high atomic utilization. Such a distinctive nanostructure endows the material with high electrocatalytic performances for CO₂ reduction to formate with near-unity Faradaic selectivity (>95%) in a wide potential window from -0.78 to -1.18 V. Furthermore, this micro/nanoreactor can give the high current densities over 300 mA cm^-2 at low applied potentials without compromising selectivity in a flow cell reactor. Density functional theory (DFT) and in situ attenuated total reflection-infrared spectroscopy (in situ ATR-IR) were further conducted to interpret the CO₂RR mechanisms.

Single-Atom and Dual-Atom Electrocatalysts Derived from Metal Organic Frameworks: Current Progress and Perspectives

Single-atom catalysts (SACs) have attracted increasing research interests owing to their unique electronic structures, quantum size effects and maximum utilization rate of atoms. Metal organic frameworks (MOFs) are good candidates to prepare SACs owing to the atomically dispersed metal nodes in MOFs and abundant N and C species to stabilize the single atoms. In addition, the distance of adjacent metal atoms can be turned by adjusting the size of ligands and adding volatile metal centers to promote the formation of isolated metal atoms. Moreover, the diverse metal centers in MOFs can promote the preparation of dual-atom catalysts (DACs) to improve the metal loading and optimize the electronic structures of the catalysts. The applications of MOFs derived SACs and DACs for electrocatalysis, including oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, carbon dioxide reduction reaction and nitrogen reduction reaction are systematically summarized in this Review. The corresponding synthesis strategies, atomic structures and electrocatalytic performances of the catalysts are discussed to provide a deep understanding of MOFs-based atomic electrocatalysts. The catalytic mechanisms of the catalysts are presented, and the crucial challenges and perspectives are proposed to promote further design and applications of atomic electrocatalysts.

Covalent Amine Tethering on Ketone Modified Porous Organic Polymers for Enhanced CO2 Capture

Effective removal of excess greenhouse gas CO₂ necessitates new adsorbents that can overcome the shortcomings of the current capture methods. To achieve that, porous materials are often modified post-synthetically with reactive amine functionalities but suffer from significant surface area losses. Herein, we report a successful amine post-functionalization of a highly porous covalent organic polymer, COP-130, without losing much porosity. By varying the amine substituents, we recorded a remarkable increase in CO₂ uptake and selectivity. Ketone functionality, a rarely accessible functional group for porous polymers, was inserted prior to amination and led to covalent tethering of amines. Interestingly, aminated polymers demonstrated relatively low heats of adsorption, which is useful for the rapid recyclability of materials, due to the formation of suspected intramolecular hydrogen bonding.

Highly Efficient and Selective CO2 Electro-Reduction to HCOOH on Sn Particle-Decorated Polymeric Carbon Nitride

Electrochemical conversion of CO₂ into liquid fuels by efficient and earth-abundant catalysts is of broad interest but remains a great challenge in renewable energy production and environmental remediation. Herein, a Sn particle-decorated polymeric carbon nitride (CN) electrocatalyst was successfully developed for efficient, durable, and highly selective CO₂ reduction to formic acid. High-resolution X-ray photoelectron spectroscopy confirmed that the metallic Sn particles and CN matrix are bound by strong chemical interaction, rendering the composite catalyst a stable structure. More notably, the electronic structure of Sn was well tuned to be highly electron-rich due to the electron transfer from N atoms of CN to Sn atoms via metal-support interactions, which favored the adsorption and activation of CO₂ molecules, promoted charge transport, and thus enhanced the electrochemical conversion of CO₂ . The composite electrocatalyst demonstrated an excellent Faradaic efficiency of formic acid (FE_HCOOH ) up to 96±2 % at the potential of -0.9 V vs. reversible hydrogen electrode, which remained at above 92 % during the electrochemical reaction of 10 h, indicating that the present Sn particle-decorated polymeric carbon nitride electrocatalyst is among the best in comparison with reported Sn-based electrocatalysts.