Highly Tensile Strained Cu(100) Surfaces by Epitaxial Grown Hexagonal Boron Nitride for CO2 Electroreduction to C2+ Products.

Copper (Cu) has been considered as the most promising catalyst for the electrochemical conversion of CO2 to multicarbon (C2+) products. However, insufficient coverage of the *CO intermediate on the C2+ formation Cu(100) facet largely hinders the C-C coupling process and thus the C2+ conversion efficiency. Herein, we developed an epitaxial growth strategy to generate highly tensile-strained Cu(100) facets via the epitaxial growth of hexagonal boron nitride (hBN) on Cu(100) facets to promote *CO coverage for efficient CO2 to C2+ conversion. The highest ∼6% tensile strain on the Cu(100) facets was obtained by lattice mismatch between the Cu(100) and hBN(002) facets. Theory calculations indicated that tensile-strained Cu(100) facets deliver a notable d-band center upshift to enhance *CO adsorption. As a result, the obtained highly tensile-strained Cu(100) facets enabled an 8-fold improvement of *CO coverage and thus a 83.4% C2+ Faradaic efficiency at 1.2 A cm-2 in strongly acidic electrolyte (pH = 1).

Identification of Synergies in Fe, Co-Coordinated Polyphthalocyanines Scaffolds for Electrochemical CO2 Reduction Reaction.

The synergistic interaction between the isolated metal sites promoted the electrocatalytic activity of the catalysts. However, the structural heterogeneity of the isolated sites makes it challenging to evaluate this effect accurately. In this work, metal-coordinated polyphthalocyanine molecules (Fe-PPc, Co-PPc, FeCo-PPc) with long-range ordered and precise coordination structures are used as a platform to study the synergies of different isolated metal sites in the electrochemical CO2 reduction reaction. The combination means of experimental and theoretical calculation clearly reveal that the coexistence of Fe and Co sites in PPc significantly enhances the conjugation effect of the macrocycle. This enhancement subsequently causes the metal sites to lose more electrons, thereby improving their adsorption of CO2 and facilitating the formation of intermediate *COOH on them. As a result, FeCo-PPc achieves a CO partial current density of about 57.4 mA/cm2 with a high turnover frequency of over 49000 site-1 h-1 at -0.9 V (vs RHE).

Copper as an Electron Hunter for Enhancing Bi2O2CO3 Electrocatalytic CO2 Conversion to Formate.

Cu-doped Bi2O2CO3 catalyst with copper (Cu) acting an electron hunter for conversion of carbon dioxide into formate is developed. The Cu-Bi2O2CO3 catalyst with hollow microsphere structure extends the duration of CO2 retention on the catalyst, providing a greater number of active sites. It exhibits remarkable performance with conversion efficacy of 98.5% and current density of 800 mA cm-2 across a wide potential window (-0.8 to -1.3 V vs RHE). Density functional theory investigations reveal that the presence of copper (Cu) significantly enhances the charge density at the active sites and influences the local electronic structure of bismuth (Bi), thereby reducing the energy barrier associated with the transformation of *OCHO species into formate.

Revealing a Double-Volcano-Like Structure-Activity Relationship for Substitution-Functionalized Metal-Phthalocyanine Catalysts toward Electrochemical CO2 Reduction.

Electron-donating/-withdrawing groups (EDGs/EWGs) substitution is widely used to regulate the catalytic performance of transition-metal phthalocyanine (MPc) toward electrochemical CO2 reduction, but the corresponding structure-activity relationships and regulation mechanisms are still ambiguous. Herein, by investigating a series of substitution-functionalized MPc (MPc-X), this work reveals a double-volcano-like relationship between the electron-donating/-withdrawing abilities of the substituents and the catalytic activities of MPc-X. The weak-EDG/-EWG substitution enhances whereas the strong-EDG/-EWG substitution mostly lowers the CO selectivity of MPc. Experimental and calculation results demonstrate that the electronic properties of the substituents influence the symmetry and energy of the highest occupied molecular orbitals of MPc-X, which in turn determine the CO2 adsorption/activation and lead to diverse CO2 reduction pathways on the EWG or EDG substituted MPc via different CO2 adsorption modes. This work provides mechanism insights that could be guidance for the design and regulation of molecular catalysts.

Construction of Cobalt Porphyrin-Modified Cu2O Nanowire Array as a Tandem Electrocatalyst for Enhanced CO2 Reduction to C2 Products.

Here, the molecule-modified Cu-based array is first constructed as the self-supporting tandem catalyst for electrocatalytic CO2 reduction reaction (CO2RR) to C2 products. The modification of cuprous oxide nanowire array on copper mesh (Cu2O@CM) with cobalt(II) tetraphenylporphyrin (CoTPP) molecules is achieved via a simple liquid phase method. The systematical characterizations confirm that the formation of axial coordinated Co-O-Cu bond between Cu2O and CoTPP can significantly promote the dispersion of CoTPP molecules on Cu2O and the electrical properties of CoTPP-Cu2O@CM heterojunction array. Consequently, as compared to Cu2O@CM array, the optimized CoTPP-Cu2O@CM sample as electrocatalyst can realize the 2.08-fold C2 Faraday efficiency (73.2% vs 35.2%) and the 2.54-fold current density (‒52.9 vs ‒20.8 mA cm-2) at ‒1.1 V versus RHE in an H-cell. The comprehensive performance is superior to most of the reported Cu-based materials in the H-cell. Further study reveals that the CoTPP adsorption on Cu2O can restrain the hydrogen evolution reaction, improve the coverage of *CO intermediate, and maintain the existence of Cu(I) at low potential.

Carbon Catalysts Empowering Sustainable Chemical Synthesis via Electrochemical CO2 Conversion and Two-Electron Oxygen Reduction Reaction.

Carbon materials hold significant promise in electrocatalysis, particularly in electrochemical CO2 reduction reaction (eCO2 RR) and two-electron oxygen reduction reaction (2e- ORR). The pivotal factor in achieving exceptional overall catalytic performance in carbon catalysts is the strategic design of specific active sites and nanostructures. This work presents a comprehensive overview of recent developments in carbon electrocatalysts for eCO2 RR and 2e- ORR. The creation of active sites through single/dual heteroatom doping, functional group decoration, topological defect, and micro-nano structuring, along with their synergistic effects, is thoroughly examined. Elaboration on the catalytic mechanisms and structure-activity relationships of these active sites is provided. In addition to directly serving as electrocatalysts, this review explores the role of carbon matrix as a support in finely adjusting the reactivity of single-atom molecular catalysts. Finally, the work addresses the challenges and prospects associated with designing and fabricating carbon electrocatalysts, providing valuable insights into the future trajectory of this dynamic field.

Metal-Organic Framework Derived Bi-O-Sn/C Nanostructure: Tailoring the Adsorption Site of Dominant Intermediate for Highly Efficient CO2 Electroreduction to Formate.

Electrochemical CO2 reduction into high-value-added formic acid/formate is an attractive strategy to mitigate global warming and achieve energy sustainability. However, the adsorption energy of most catalysts for the key intermediate *OCHO is usually weak, and how to rationally optimize the adsorption of *OCHO is challenging. Here, an effective Bi-Sn bimetallic electrocatalyst (Bi1 -O-Sn1 @C) where a Bi-O-Sn bridge-type nanostructure is constructed with O as an electron bridge is reported. The electronic structure of Sn is precisely tuned by electron transfer from Bi to Sn through O bridge, resulting in the optimal adsorption energy of intermediate *OCHO on the surface of Sn and the enhanced activity for formate production. Thus, the Bi1 -O-Sn1 @C exhibits an excellent Faradaic efficiency (FE) of 97.7% at -1.1 V (vs RHE) for CO2 reduction to formate (HCOO- ) and a high current density of 310 mA cm-2 at -1.5 V, which is one of the best results catalyzed by Bi- and Sn-based catalysts reported previously. Impressively, the FE exceeds 93% at a wide potential range from -0.9 to -1.4 V. In-situ ATR-FTIR, in-situ Raman, and DFT calculations confirm the unique role of the bridge-type structure of Bi-O-Sn in highly efficient electrocatalytic reduction of CO2 into formate.

Revealing the structure of the active sites for the electrocatalytic CO2 reduction to CO over Co single atom catalysts using operando XANES and machine learning.

Transition-metal nitrogen-doped carbons (TM-N-C) are emerging as a highly promising catalyst class for several important electrocatalytic processes, including the electrocatalytic CO2 reduction reaction (CO2RR). The unique local environment around the singly dispersed metal site in TM-N-C catalysts is likely to be responsible for their catalytic properties, which differ significantly from those of bulk or nanostructured catalysts. However, the identification of the actual working structure of the main active units in TM-N-C remains a challenging task due to the fluctional, dynamic nature of these catalysts, and scarcity of experimental techniques that could probe the structure of these materials under realistic working conditions. This issue is addressed in this work and the local atomistic and electronic structure of the metal site in a Co-N-C catalyst for CO2RR is investigated by employing time-resolved operando X-ray absorption spectroscopy (XAS) combined with advanced data analysis techniques. This multi-step approach, based on principal component analysis, spectral decomposition and supervised machine learning methods, allows the contributions of several co-existing species in the working Co-N-C catalysts to be decoupled, and their XAS spectra deciphered, paving the way for understanding the CO2RR mechanisms in the Co-N-C catalysts, and further optimization of this class of electrocatalytic systems.

Understanding the Electrochemical Carbon Dioxide Reduction Reaction Mechanism of Lattice Tuning of Copper by Silver Single-Crystal Surface.

Intermolecular interactions and adsorbate coverage on a metal electrode's surface/interface play an important role in CO2 reduction reaction (CO2RR). Herein, the activity and selectivity of CO2RR on bimetallic electrode, where a full monoatomic Cu layer covers on Ag surface (CuML/Ag) are investigated by using density functional theory calculations. The surface geometric and electronic structure results indicate that there is high electrocatalytic activity for CO2RR on the CuML/Ag electrode. Specifically, the CuML/Ag surface can accelerate the H2O and CO2 adsorption and hydrogenation while lowering the reaction energy of the rate-determining step. The structure parameters of chemisorbed CO2 with and without H2O demonstrate that activated H2O not only promotes the C-O dissociation but also provides the protons required for CO2RR on the CuML/Ag electrode surface. Furthermore, the various reaction mechanism diagrams indicate that the CuML/Ag electrode has high selectivity for CO2RR, and the efficiency of products can be regulated by modulating the reaction's electric potential.

Silica-Derived Nanostructured Electrode Materials for ORR, OER, HER, CO2RR Electrocatalysis, and Energy Storage Applications: A Review.

Silica-derived nanostructured catalysts (SDNCs) are a class of materials synthesized using nanocasting and templating techniques, which involve the sacrificial removal of a silica template to generate highly porous nanostructured materials. The surface of these nanostructures is functionalized with a variety of electrocatalytically active metal and non-metal atoms. SDNCs have attracted considerable attention due to their unique physicochemical properties, tunable electronic configuration, and microstructure. These properties make them highly efficient catalysts and promising electrode materials for next generation electrocatalysis, energy conversion, and energy storage technologies. The continued development of SDNCs is likely to lead to new and improved electrocatalysts and electrode materials. This review article provides a comprehensive overview of the recent advances in the development of SDNCs for electrocatalysis and energy storage applications. It analyzes 337,061 research articles published in the Web of Science (WoS) database up to December 2022 using the keywords "silica", "electrocatalysts", "ORR", "OER", "HER", "HOR", "CO2RR", "batteries", and "supercapacitors". The review discusses the application of SDNCs for oxygen reduction reaction (ORR), oxygen evolution reaction (OER), hydrogen evolution reaction (HER), carbon dioxide reduction reaction (CO2RR), supercapacitors, lithium-ion batteries, and thermal energy storage applications. It concludes by discussing the advantages and limitations of SDNCs for energy applications.

Bifunctional electrocatalytic reduction performance of nitrogen containing biomass based nanoreactors loaded with Ni nanoparticles for oxygen and carbon dioxide.

In the face of increasing energy demand, the approach of transformation that combines energy restructuring and environmental governance has become a popular research direction. As an important part of electrocatalytic reactions for gas molecules, reduction reactions of oxygen (ORR) and carbon dioxide (CO2RR) are very indispensable in the field of energy conversion and storage. However, the non-interchangeability and irreversibility of electrode materials have always been a challenge in electrocatalysis. Hereon, nickel and nitrogen decorated biomass carbon-based materials (Ni/N-BC) has been prepared by high temperature pyrolysis using agricultural waste straw as raw material. Surprisingly, it possesses abundant active sites and specific surface area as a bifunctional electrocatalyst for ORR and CO2RR. The three-dimensional porous cavity structure for the framework of biomass could not only provide a strong anchoring foundation for the active site, but also facilitate the transport and enrichment of reactants around the site. In addition, temperature modulation during the preparation process also optimizes the composition and structure of biomass carbon and nitrogen. Benefit from above structure and morphology advantages, Ni/N-BC-800 exhibits the superior electrocatalytic activity for both ORR and CO2RR simultaneously. More specifically, Ni/N-BC-800 exhibits satisfactory ORR activity in terms of initial potential and half wave potential, while also enables the production of CO under high selective. The research results provide ideas for the development and design of electrode materials and green electrocatalysts, and also expand new applications of agricultural waste in fields such as energy conversion, environmental protection, and resource utilization.

Probing the Roles of Indium Oxides on Copper Catalysts for Enhanced Selectivity during CO2-to-CO Electrochemical Reduction.

The electrochemical CO2 reduction reaction (CO2RR) provides an alternative protocol to producing industrial chemicals with renewable electricity sources, and the highly selective, durable, and economic catalysts should expedite CO2RR applications. Here, we demonstrate a composite Cu-In2O3 catalyst in which a trace amount of In2O3 decorated on Cu surface greatly improves the selectivity and stability for CO2-to-CO reduction as compared to the counterparts (Cu or In2O3), realizing a CO faradaic efficiency (FECO) of 95% at -0.7 V (vs RHE) and no obvious degradation within 7 h. In situ X-ray absorption spectroscopy reveals that In2O3 undergoes the redox reaction and preserves the metallic state of Cu during the CO2RR process. Strong electronic interaction and coupling occur at the Cu/In2O3 interface which serves as the active site for selective CO2RR. Theoretical calculation confirms the roles of In2O3 in preventing oxidation and altering the electronic structure of Cu to assist COOH* formation and demote CO* adsorption at the Cu/In2O3 interface.

Charge-Separated Pdδ--Cuδ+ Atom Pairs Promote CO2 Reduction to C2.

Positively charged Cu sites have been confirmed to significantly promote the production of multicarbon (C2) products from an electrochemical CO2 reduction reaction (CO2RR). However, the positively charged Cu has difficulty in existing under a strong negative bias. In this work, we design a Pdδ--Cu3N catalyst containing charge-separated Pdδ--Cuδ+ atom pair that can stabilize the Cuδ+ sites. In situ characterizations and density functional theory reveal that the first reported negatively charged Pdδ- sites exhibited a superior CO binding capacity together with the adjacent Cuδ+ sites, synergistically promoting the CO dimerization process to produce C2 products. As a result, we achieve a 14-fold increase in the C2 product Faradaic efficiency (FE) on Pdδ--Cu3N, from 5.6% to 78.2%. This work provides a new strategy for synthesizing negative valence atom-pair catalysts and an atomic-level modulation approach of unstable Cuδ+ sites in the CO2RR.

Oxygen atom activated ZIF-67/carbon cloth in plasma system for CO2 reduction.

ZIF-67 was grown in situ on carbon cloth (CC) using a simple one-step method. The prepared ZIF-67/CC electrodes exhibited excellent CO2 reduction reaction (CO2RR) performance in a dielectric barrier discharge plasma reactor. The highest concentrations of produced formic acid and formaldehyde were 9.16 and 0.068 mmol L-1 at a reaction time of 1 h, respectively. The high performance is related to the unique high aspect ratio structure and pad-like cavity of ZIF-67, which results not only in an increase in the specific surface area for CO2 adsorption but also in the hydrophobicity of the electrode. Unexpectedly, the superoxide radical (·O2-) greatly affects the reduction performance of the electrode. In addition, the ZIF-67/CC electrode maintained good CO2RR performance in the presence of different pollutants, and the production of formic acid and formaldehyde increased to 10.81 and 0.11 mmol L-1 at 1 h with the addition of 10 mg L-1 phenol. This research provides new directions in the field of plasma catalysis.

Hydrochar from Pine Needles as a Green Alternative for Catalytic Electrodes in Energy Applications.

Hydrothermal carbonization (HTC) serves as a sustainable method to transform pine needle waste into nitrogen-doped (N-doped) hydrochars. The primary focus is on evaluating these hydrochars as catalytic electrodes for the oxygen reduction reaction (ORR) and carbon dioxide reduction reaction (CO2RR), which are pivotal processes with significant environmental implications. Hydrochars were synthesized by varying the parameters such as nitrogen loading, temperature, and residence time. These materials were then thoroughly characterized using diverse analytical techniques, including elemental analysis, density measurements, BET surface area analysis, and spectroscopies like Raman, FTIR, and XPS, along with optical and scanning electron microscopies. The subsequent electrochemical assessment involved preparing electrocatalytic inks by combining hydrochars with an anion exchange ionomer (AEI) to leverage their synergistic effects. To the best of our knowledge, there are no previous reports on catalytic electrodes that simultaneously incorporate both a hydrochar and AEI. Evaluation metrics such as current densities, onset and half-wave potentials, and Koutecky-Levich and Tafel plots provided insights into their electrocatalytic performances. Notably, hydrochars synthesized at 230 °C exhibited an onset potential of 0.92 V vs. RHE, marking the highest reported value for a hydrochar. They also facilitated the exchange of four electrons at 0.26 V vs. RHE in the ORR. Additionally, the CO2RR yielded valuable C2 products like acetaldehyde and acetate. These findings highlight the remarkable electrocatalytic activity of the optimized hydrochars, which could be attributed, at least in part, to their optimal porosity.

Bi/CeO2-Decorated CuS Electrocatalysts for CO2-to-Formate Conversion.

The electrocatalytic carbon dioxide (CO2) reduction reaction (CO2RR) is extensively regarded as a promising strategy to reach carbon neutralization. Copper sulfide (CuS) has been widely studied for its ability to produce C1 products with high selectivity. However, challenges still remain owing to the poor selectivity of formate. Here, a Bi/CeO2/CuS composite was synthesized using a simple solvothermal method. Bi/CeO2-decorated CuS possessed high formate selectivity, with the Faraday efficiency and current density reaching 88% and 17 mA cm-2, respectively, in an H-cell. The Bi/CeO2/CuS structure significantly reduces the energy barrier formed by OCHO*, resulting in the high activity and selectivity of the CO2 conversion to formate. Ce4+ readily undergoes reduction to Ce3+, allowing the formation of a conductive network of Ce4+/Ce3+. This network facilitates electron transfer, stabilizes the Cu+ species, and enhances the adsorption and activation of CO2. Furthermore, sulfur catalyzes the OCHO* transformation to formate. This work describes a highly efficient catalyst for CO2 to formate, which will aid in catalyst design for CO2RR to target products.

Effects of Iron Species on Low Temperature CO2 Electrolyzers.

Electrochemical energy conversion devices are considered key in reducing CO2 emissions and significant efforts are being applied to accelerate device development. Unlike other technologies, low temperature electrolyzers have the ability to directly convert CO2 into a range of value-added chemicals. To make them commercially viable, however, device efficiency and durability must be increased. Although their design is similar to more mature water electrolyzers and fuel cells, new cell concepts and components are needed. Due to the complexity of the system, singular component optimization is common. As a result, the component interplay is often overlooked. The influence of Fe-species clearly shows that the cell must be considered holistically during optimization, to avoid future issues due to component interference or cross-contamination. Fe-impurities are ubiquitous, and their influence on single components is well-researched. The activity of non-noble anodes has been increased through the deliberate addition of iron. At the same time, however, Fe-species accelerate cathode and membrane degradation. Here, we interpret literature on single components to gain an understanding of how Fe-species influence low temperature CO2 electrolyzers holistically. The role of Fe-species serves to highlight the need for considerations regarding component interplay in general.

Switching Reaction Pathways of CO2 Electroreduction by Modulating Cations in the Electrochemical Double Layer.

Tuning the selectivity of CO2 electroreduction reaction (CO2RR) solely by changing electrolyte is a very attractive topic. In this study, we conducted CO2RR in different aqueous electrolytes over bulk metal electrodes. It was discovered that controlled CO2RR could be achieved by modulating cations in the electrochemical double layer. Specifically, ionic liquid cations in the electrolyte significantly inhibits the hydrogen evolution reaction (HER), while yielding high Faraday efficiencies toward CO (FECO) or formate (FEformate) depending on the alkali metal cations. For example, the product could be switched from CO (FECO=97.3 %) to formate (FEformate=93.5 %) by changing the electrolyte from 0.1 M KBr-0.5 M 1-octyl-3-methylimidazolium bromide (OmimBr) to 0.1 M CsBr-0.5 M OmimBr aqueous solutions over pristine Cu foil electrode. In situ spectroscopy and theoretical calculations reveal that the ordered structure generated by the assembly of Omim+ under an applied negative potential alters the hydrogen bonding structure of the interfacial water, thereby inhibiting the HER. The difference in selectivity in the presence of different cations is attributed to the hydrogen bonding effect caused by Omim+, which alters the solvated structure of the alkali metal cations and thus affects the stabilization of intermediates of different pathways.

Deciphering Structure-Activity Relationship Towards CO2 Electroreduction over SnO2 by A Standard Research Paradigm.

Authentic surface structures under reaction conditions determine the activity and selectivity of electrocatalysts, therefore, the knowledge of the structure-activity relationship can facilitate the design of efficient catalyst structures for specific reactivity requirements. However, understanding the relationship between a more realistic active surface and its performance is challenging due to the complicated interface microenvironment in electrocatalysis. Herein, we proposed a standard research paradigm to effectively decipher the structure-activity relationship in electrocatalysis, which is exemplified in the CO2 electroreduction over SnO2 . The proposed practice has aided in discovering authentic/resting surface states (Sn layer) of SnO2 accountable for the electrochemical CO2 reduction reaction (CO2 RR) performance under electrocatalytic conditions, which then is corroborated in the subsequent CO2 RR experiments over SnO2 with different morphologies (nanorods, nanoparticles, and nanosheets) in combination with in situ characterizations. This proposed methodology is further extended to the SnO electrocatalysts, providing helpful insights into catalytic structures. It is believed that our proposed standard research paradigm is also applicable to other electrocatalytic systems, in the meantime, decreases the discrepancy between theory and experiments, and accelerates the design of catalyst structures that achieve sustainable performance for energy conversion.

Enhanced Electrochemical CO2 Reduction to Formate over Phosphate-Modified In: Water Activation and Active Site Tuning.

Electrochemical CO2 reduction reaction (CO2RR) offers a sustainable strategy for producing fuels and chemicals. However, it suffers from sluggish CO2 activation and slow water dissociation. In this work, we construct a (P-O)δ- modified In catalyst that exhibits high activity and selectivity in electrochemical CO2 reduction to formate. A combination of in situ characterizations and kinetic analyses indicate that (P-O)δ- has a strong interaction with K+(H2O)n, which effectively accelerates water dissociation to provide protons. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) measurements together with density functional theory (DFT) calculations disclose that (P-O)δ- modification leads to a higher valence state of In active site, thus promoting CO2 activation and HCOO* formation, while inhibiting competitive hydrogen evolution reaction (HER). As a result, the (P-O)δ- modified oxide-derived In catalyst exhibits excellent formate selectivity across a broad potential window with a formate Faradaic efficiency as high as 92.1 % at a partial current density of ~200 mA cm-2 and a cathodic potential of -1.2 V vs. RHE in an alkaline electrolyte.