Electrochemically Driven Cation Exchange Enables the Rational Design of Active CO2 Reduction Electrocatalysts

Determinants of regioselectivity of heterostructures in cation exchange reactions

A cation exchange (CE) reaction offers a remarkable opportunity to create versatile metal sulfide nanocrystals (NCs) with arbitrary complexity in composition, structure, and functionality. The concept of regioselectivity has been discovered and developed to build the target heterostructures through CE reactions, yet a general principle of regioselectivity remains unclear. In this work, we establish connections between experimental results and theoretical insights to elucidate the determinants of regioselectivity using designed aliovalent CE reactions on a two-dimensional template. Our findings demonstrate that the local density of delocalized electrons between the host lattice and guest cations determines the reaction heat on different facets, thereby dictating the resulting structure of the nanoplates after CE reactions. We unravel the mechanism of CE reactions occurring primarily at the edges of the nanoplates and manipulate the occurrence of these reactions by employing active or passivated edges. Consequently, a series of heterostructures with distinct combinations of metal sulfide phases can be synthesized by manipulating these determinants. Our work paves the way for the synthesis of copper sulfide-based heterostructures with multifunctionalities and emergent properties.

Strongly-Interacted NiSe2/NiFe2O4 Architectures Built Through Selective Atomic Migration as Catalysts for the Oxygen Evolution Reaction

The interactions between the catalyst and support are widely used in many important catalytic reactions but the construction of strong interaction with definite microenvironments to understand the structure-activity relationship is still challenging. Here, strongly-interacted composites are prepared via selective exsolution of active NiSe2 from the host matrix of NiFe2O4 (S-NiSe2/NiFe2O4) taking advantage of the differences of migration energy, in which the NiSe2 possessed both high dispersion and small size. The characteristics of spatially resolved scanning transmission X-ray microscopy (STXM) coupled with analytical Mössbauer spectra for the surface and bulk electronic structures unveiled that this strongly interacted composite triggered more charge transfers from the NiSe2 to the host of NiFe2O4 while stabilizing the inherent atomic coordination of NiFe2O4. The obtained S-NiSe2/NiFe2O4 exhibits overpotentials of 290 mV at 10 mA cm-2 for oxygen evolution reaction (OER). This strategy is general and can be extended to other supported catalysts, providing a powerful tool for modulating the catalytic performance of strongly-interacted composites.

Synergistic effects of CuS/TiO2 heterointerfaces: Enhanced cathodic CO2 reduction and anodic CH3OH oxidation for paired electrosynthesis of formate

The electrochemical reduction of carbon dioxide into energy-carrying compounds or value-added chemicals is of great significance for diminishing the greenhouse effect. However, it is still imperative to replace the less-value anodic oxygen evolution reaction (OER) to improve the technical economy. Herein, we firstly reported a bifunctional CuS/TiO2 catalyst for both anodic methanol oxidation reaction (MOR) and cathodic carbon dioxide reduction (CO2R). The in-built abundant CuS/TiO2 heterointerfaces are found to boost the CO2R and MOR to produce formate. Based on the unique bifunctionality of CuS/TiO2, a paired electrosynthesis of formate was performed with a total Faradaic efficiency (FE) of about 170 %, in which the cathodic CO2R achieved a formate FE of about 70 %, and the anodic MOR exhibited an almost 100 % formate FE.

Recent advances in copper chalcogenides for CO2 electroreduction

Transforming CO2 through electrochemical methods into useful chemicals and energy sources may contribute to solutions for global energy and ecological challenges. Copper chalcogenides exhibit unique properties that make them potential catalysts for CO2 electroreduction. In this review, we provide an overview and comment on the latest advances made in the synthesis, characterization, and performance of copper chalcogenide materials for CO2 electroreduction, focusing on the work of the last five years. Strategies to boost their performance can be classified in three groups: (1) structural and compositional tuning, (2) leveraging on heterostructures and hybrid materials, and (3) optimizing size and morphology. Despite overall progress, concerns about selectivity and stability persist and require further investigation. This review outlines future directions for developing the next-generation of copper chalcogenide materials, emphasizing on rational design and advanced characterization techniques for efficient and selective CO2 electroreduction.

Copper-based catalysts for the electrochemical reduction of carbon dioxide: progress and future prospects

There is an urgent need for the development of high performance electrocatalysts for the CO₂ reduction reaction (CO₂RR) to address environmental issues such as global warming and achieve carbon neutral energy systems. In recent years, Cu-based electrocatalysts have attracted significant attention in this regard. The present review introduces fundamental aspects of the electrocatalytic CO₂RR process together with a systematic examination of recent developments in Cu-based electrocatalysts for the electroreduction of CO₂ to various high-value multicarbon products. Current challenges and future trends in the development of advanced Cu-based CO₂RR electrocatalysts providing high activity and selectivity are also discussed.

In-Plane BO3 Configuration in P2 Layered Oxide Enables Outstanding Long Cycle Performance for Sodium Ion Batteries

P2-phase layered cathode materials with distinguished electrochemical performance for sodium-ion batteries have attracted extensive attention, but they face critical challenges of transition metal layer sliding and unfavorable formation of hydration phase upon cycling, thus showing inferior long cycle life. Herein, a new approach is reported to modulate the local structure of P2 material by constructing a state-of-the-art in-plane BO₃ triangle configuration ((Na_0.67 Ni_0.3 Co_0.1 Mn_0.6 O_1.94 (BO₃ )_0.02 ). Both are unveiled experimentally and theoretically that such a structure can serve as a robust pillar to hold up the entire structure, by inhibiting the H₂ O insertion upon Na (de)intercalation and preventing the structure from deformation, which significantly boost the long cycle capability of P2-materials. Meanwhile, more Na ions in the architecture are enabled to site on the edge sharing octahedrons (Na_e ), thus benefiting the Na⁺ transportation. Consequently, the as produced material demonstrates an ultralow volume variation (1.8%), and an outstanding capacity retention of 80.1% after 1000 cycles at 2 C. This work sheds light on efficient architecture modulation of layered oxides through proper nonmetallic element doping.

Alloying strategies for tuning product selectivity during electrochemical CO2 reduction over Cu

Excessive reliance on fossil fuels has led to the release and accumulation of large quantities of CO₂ into the atmosphere which has raised serious concerns related to environmental pollution and global warming. One way to mitigate this problem is to electrochemically recycle CO₂ to value-added chemicals or fuels using electricity from renewable energy sources. Cu is the only metallic electrocatalyst that has been shown to produce a wide range of industrially important chemicals at appreciable rates. However, low product selectivity is a fundamental issue limiting commercial applications of electrochemical CO₂ reduction over Cu catalysts. Combining copper with other metals that actively contribute to the electrochemical CO₂ reduction reaction process can selectively facilitate generation of desirable products. Alloying Cu can alter surface binding strength through electronic and geometric effects, enhancing the availability of surface confined carbon species, and stabilising key reduction intermediates. As a result, significant research has been undertaken to design and fabricate copper-based alloy catalysts with structures that can enhance the selectivity of targeted products. In this article, progress with use of alloying strategies for development of Cu-alloy catalysts are reviewed. Challenges in achieving high selectivity and possible future directions for development of new copper-based alloy catalysts are considered.

Hierarchical S-modified Cu porous nanoflakes for efficient CO2 electroreduction to formate

Electrochemical reduction of CO₂ into liquid fuels is a promising approach to achieving a carbon-neutral energy cycle but remains a great challenge due to the lack of efficient catalysts. Here, the hierarchical architectures assembled by ultrathin and porous S-modified Cu nanoflakes (Cu-S NFs) are designed and constructed as an efficient electrocatalyst for CO₂ conversion to formate with high partial current density. Specifically, when integrated into a gas diffusion electrode in a flow cell, Cu-S NFs are capable of delivering the ultrahigh formate current density up to 404.1 mA cm^-2 with a selectivity of 89.8%. Electrochemical tests and theoretical calculations indicate that the superior performance of the designed catalysts may be attributed to the unique structure, which can provide abundant active sites, fast charge transfer, and highly active edge sites.

Splicing the active phases of copper/cobalt-based catalysts achieves high-rate tandem electroreduction of nitrate to ammonia

Electrocatalytic recycling of waste nitrate (NO₃⁻) to valuable ammonia (NH₃) at ambient conditions is a green and appealing alternative to the Haber−Bosch process. However, the reaction requires multi-step electron and proton transfer, making it a grand challenge to drive high-rate NH₃ synthesis in an energy-efficient way. Herein, we present a design concept of tandem catalysts, which involves coupling intermediate phases of different transition metals, existing at low applied overpotentials, as cooperative active sites that enable cascade NO₃⁻-to-NH₃ conversion, in turn avoiding the generally encountered scaling relations. We implement the concept by electrochemical transformation of Cu−Co binary sulfides into potential-dependent core−shell Cu/CuO_x and Co/CoO phases. Electrochemical evaluation, kinetic studies, and in−situ Raman spectra reveal that the inner Cu/CuO_x phases preferentially catalyze NO₃⁻ reduction to NO₂⁻, which is rapidly reduced to NH₃ at the nearby Co/CoO shell. This unique tandem catalyst system leads to a NO₃⁻-to-NH₃ Faradaic efficiency of 93.3 ± 2.1% in a wide range of NO₃⁻ concentrations at pH 13, a high NH₃ yield rate of 1.17 mmol cm⁻² h⁻¹ in 0.1 M NO₃⁻ at −0.175 V vs. RHE, and a half-cell energy efficiency of ~36%, surpassing most previous reports.

Electrocatalytic recycling of waste nitrate to NH₃ under ambient conditions maybe an appealing alternative to the Haber−Bosch process. Here the authors report a tandem catalyst system involving cooperative adsorption of reaction intermediate on different transition metal active sites for nitrate electroreduction with high efficiency.

Metal-Organic Frameworks Derived Electrocatalysts for Oxygen and Carbon Dioxide Reduction Reaction

The increasing demands of energy and environmental concerns have motivated researchers to cultivate renewable energy resources for replacing conventional fossil fuels. The modern energy conversion and storage devices required high efficient and stable electrocatalysts to fulfil the market demands. In previous years, we are witness for considerable developments of scientific attention in Metal-organic Frameworks (MOFs) and their derived nanomaterials in electrocatalysis. In current review article, we have discussed the progress of optimistic strategies and approaches for the manufacturing of MOF-derived functional materials and their presentation as electrocatalysts for significant energy related reactions. MOFs functioning as a self-sacrificing template bid different benefits for the preparation of metal nanostructures, metal oxides and carbon-abundant materials promoting through the porous structure, organic functionalities, abundance of metal sites and large surface area. Thorough study for the recent advancement in the MOF-derived materials, metal-coordinated N-doped carbons with single-atom active sites are emerging candidates for future commercial applications. However, there are some tasks that should be addressed, to attain improved, appreciative and controlled structural parameters for catalytic and chemical behavior.

Electronic structure modulation of bismuth catalysts induced by sulfur and oxygen co-doping for promoting CO2 electroreduction

Carbon dioxide electroreduction into green fuels and value-added chemicals is an attractive method for the utilization of renewable energy to mitigate global warming. High-efficiency catalysts are necessary for mild and...

Highly Controllable Hierarchically Porous Ag/Ag2 S Heterostructure by Cation Exchange for Efficient Hydrogen Evolution

Establishing the hierarchical porous architectures has been considered to be the most efficient approach to realize the efficient mass diffusion and large exposed active sites of designed micro/nanomaterial catalysts for hydrogen evolution reactions (HER). In this work, the nonequivalent cation exchange strategy is developed to fabricate the hierarchically porous Ag/Ag₂ S heterostructure based on the rapid cation exchange by the metal-organic framework (MOF)-derived CoS. The as-prepared Ag/Ag₂ S inherits the original 3D hollow morphology of CoS with porous nature, possessing abundant S-vacancies and lattice strain simultaneously due to the coordination loss and in-situ epitaxial growth of metallic Ag on the surface. Owing to the optimizations of lattice and electronic structures, the unique hierarchically porous Ag/Ag₂ S heterostructure exhibits superior catalytic performance than previously reported catalysts derived from MOF. Theoretical calculations have confirmed that the co-existence of Ag cluster and sulfur vacancies activates the electroactivity of the interfacial defective region to boost the HER process. The binding strength of the proton and energetic trend of HER has been optimized with the formation of Ag/Ag₂ S heterostructure, which guarantees the efficient generation of H₂ . This study opens a new strategy for the utilization of the nonequivalent cation exchange strategy to efficiently synthesize advanced electrocatalysts with high performances.

A Facile Strategy for Constructing a Carbon-Particle-Modified Metal-Organic Framework for Enhancing the Efficiency of CO2 Electroreduction into Formate

Electrocatalytic reduction of CO₂ by metal-organic frameworks (MOFs) has been widely investigated, but insufficient conductivity limits application. Herein, a porous 3D In-MOF {(Me₂ NH₂ )[In(BCP)]⋅2 DMF}_n (V11) with good stability was constructed with two types of channels (1.6 and 1.2 nm diameter). V11 exhibits moderate catalytic activity in CO₂ electroreduction with 76.0 % of Faradaic efficiency for formate (FE_HCOO- ). Methylene blue molecules of suitable size and pyrolysis temperature were introduced and transformed into carbon particles (CPs) after calcination. The performance of the obtained CPs@V11 is significantly improved both in FE_HCOO- (from 76.0 % to 90.1 %) and current density (2.2 times). Control experiments show that introduced CPs serve as accelerant to promote the charges and mass transfer in framework, and benefit to sufficiently expose active sites. This strategy can also work on other In-MOFs, demonstrating the universality of this method for electroreduction of CO₂ .

In Situ Phase Separation into Coupled Interfaces for Promoting CO2 Electroreduction to Formate over a Wide Potential Window

Bimetallic sulfides are expected to realize efficient CO₂ electroreduction into formate over a wide potential window, however, they will undergo in situ structural evolution under the reaction conditions. Therefore, clarifying the structural evolution process, the real active site and the catalytic mechanism is significant. Here, taking Cu₂ SnS₃ as an example, we unveiled that Cu₂ SnS₃ occurred self-adapted phase separation toward forming the stable SnO₂ @CuS and SnO₂ @Cu₂ O heterojunction during the electrochemical process. Calculations illustrated that the strongly coupled interfaces as real active sites driven the electron self-flow from Sn⁴⁺ to Cu⁺ , thereby promoting the delocalized Sn sites to combine HCOO* with H*. Cu₂ SnS₃ nanosheets achieve over 83.4 % formate selectivity in a wide potential range from -0.6 V to -1.1 V. Our findings provide insight into the structural evolution process and performance-enhanced origin of ternary sulfides under the CO₂ electroreduction.

Linking the Dynamic Chemical State of Catalysts with the Product Profile of Electrocatalytic CO2 Reduction

The promoted activity and enhanced selectivity of electrocatalysts is commonly ascribed to specific structural features such as surface facets, morphology, and atomic defects. However, unraveling the factors that really govern the direct electrochemical reduction of CO₂ (CO₂ RR) is still very challenging since the surface state of electrocatalysts is dynamic and difficult to predict under working conditions. Moreover, theoretical predictions from the viewpoint of thermodynamics alone often fail to specify the actual configuration of a catalyst for the dynamic CO₂ RR process. Herein, we re-survey recent studies with the emphasis on revealing the dynamic chemical state of Cu sites under CO₂ RR conditions extracted by in situ/operando characterizations, and further validate a critical link between the chemical state of Cu and the product profile of CO₂ RR. This point of view provides a generalizable concept of dynamic chemical-state-driven CO₂ RR selectivity that offers an inspiration in both fundamental understanding and efficient electrocatalysts design.

An Investigation of Active Sites for electrochemical CO2 Reduction Reactions: From In Situ Characterization to Rational Design

The electrochemical carbon dioxide (CO2) reduction reaction (CO2RR) is among the most promising approaches used to transform greenhouse gas into useful fuels and chemicals. However, the reaction suffers from low selectivity, high overpotential, and low reaction rate. Active site identification in the CO2RR is vital for the understanding of the reaction mechanism and the rational development of new electrocatalysts with both high selectivity and stability. Herein, in situ characterization monitoring of active sites during the reaction is summarized and a general understanding of active sites on the various catalysts in the CO2RR, including metal-based catalysts, carbon-based catalysts, and metal-organic frameworks-based electrocatalysts is updated. For each type of electrocatalysts, the reaction pathway and real active sites are proposed based on in situ characterization techniques and theoretical calculations. Finally, the key limitations and challenges observed for the electrochemical fixation of CO2 is presented. It is expected that this review will provide new insights and directions into further scientific development and practical applicability of CO2 electroreduction.

An Efficient Interfacial Synthesis of Two-Dimensional Metal-Organic Framework Nanosheets for Electrochemical Hydrogen Peroxide Production

Two-dimensional (2D) metal-organic framework nanosheets (MOF NSs) play a vital role in catalysis, but the most preparation is ultrasonication or solvothermal. Herein, a liquid-liquid interfacial synthesis method has been developed for the efficient fabrication of a series of 2D Ni MOF NSs. The active sites could be modulated by readily tuning the ratios of metal precursors and organic linkers (R_M/L ). The Ni MOF NSs display highly R_M/L dependent activities towards 2e oxygen reduction reaction (ORR) to hydrogen peroxide (H₂ O₂ ), where the Ni MOF NSs with the R_M/L of 6 exhibit the optimal near-zero overpotential, ca. 98 % H₂ O₂ selectivity and production rate of ca. 80 mmol g_cat ^-1  h^-1 in 0.1 M KOH. As evidenced by X-ray absorption fine structure spectroscopy, the coordination environment of active sites changed from saturation to unsaturation, and the partially unsaturated metal atoms are crucial to create optimal sites for enhancing the electrocatalysis.

Biochar-Supported BiOx for Effective Electrosynthesis of Formic Acid from Carbon Dioxide Reduction

The electrochemical reduction of carbon dioxide (CO2) to value-added chemicals and fuels has attracted worldwide interest for its potential to address various contemporary global issues such as CO2-related climate change, the earth’s carbon deficit and the energy crisis. In the development of this technology, many efforts have been focused on the design of inexpensive, eco-friendly and effective catalysts. In this work, a bismuth (Bi)-based material was simply synthesized via a scalable method and fully characterized by physical, chemical and electrochemical techniques. The catalyst material consisted of Bi/Bi2O3 nanoparticles and a biochar prevenient from the pyrolysis of brewed coffee waste. It was observed that the surface of the biochar was thoroughly decorated with nanoparticles. Due to its uniform surface, the biochar–BiOx electrode demonstrated good selectivity for CO2 reduction, showing a faradaic efficiency of more than 90% for CO and HCOOH formation in a wide potential range. Particularly, the selectivity for HCOOH reached more than 80% from −0.9 V to −1.3 V vs the reversible hydrogen electrode and peaks at 87%. Besides the selectivity, the production rate of HCOOH also achieved significant values with a maximum of 59.6 mg cm−2 h−1, implying a good application potential for biochar–BiOx material in the conversion of CO2 to HCOOH.

Metal-organic framework derived nanomaterials for electrocatalysis: recent developments for CO2 and N2 reduction

In recent years, we are witnessing a substantially growing scientific interest in MOFs and their derived materials in the field of electrocatalysis. MOFs acting as a self-sacrificing template offer various advantages for the synthesis of carbon-rich materials, metal oxides, and metal nanostructures containing graphitic carbon-based materials benefiting from the high surface area, porous structure, and abundance of metal sites and organic functionalities. Yet, despite recent advancement in the field of MOF-derived materials, there are still several significant challenges that should be overcomed, to obtain better control and understanding on the factors determining their chemical, structural and catalytic nature. In this minireview, we will discuss recently reported advances in the development of promising methods and strategies for the construction of functional MOF-derived materials and their application as highly-active electrocatalysts for two important energy-related reactions: nitrogen reduction to produce ammonia, and CO2 reduction into carbon-based fuels. Moreover, a discussion containing assessments and remarks on the possible future developments of MOF-derived materials toward efficient electrocatalysis is included.

Electrocatalysis for CO2 conversion: from fundamentals to value-added products

This timely and comprehensive review mainly summarizes advances in heterogeneous electroreduction of CO₂: from fundamentals to value-added products.

Topochemical synthesis of low-dimensional nanomaterials

Over the past several decades, nanomaterials have been extensively studied owing to having a series of unique physical and chemical properties that exceed those of conventional bulk materials. Researchers have developed a lot of strategies for the synthesis of low-dimensional nanomaterials. Among them, topochemical synthesis has attracted increasing attention because it can provide more new nanomaterials by improving and upgrading inexpensive and accessible nanomaterials. In this review, we summarize and analyze many existing topochemical synthesis methods, including selective etching, liquid phase reactions, high-temperature atmosphere reactions, electrochemically assisted methods, etc. The future direction of topochemical synthesis is also proposed.