Bi-Doped SnO Nanosheets Supported on Cu Foam for Electrochemical Reduction of CO2 to HCOOH

Enhancing microbial CO2 electrocatalysis for multicarbon reduction in a wet amine-based catholyte

Microbial CO2 electroreduction (mCO2ER) offers a promising approach for producing high-value multicarbon reductants from CO2 by combining CO2 fixing microorganisms with conducting materials (i. e., cathodes). However, the solubility and availability of CO2 in an aqueous electrolyte pose significant limitations in this system. This study demonstrates the efficient production of long-chain multicarbon reductants, specifically carotenoids (~C40), within a wet amine-based catholyte medium during mCO2ER. Optimizing the concentration of the biocompatible CO2 absorbent, monoethanolamine (MEA), led to enhanced CO2 fixation in the electroautotroph bacteria. Molecular biological analyses revealed that MEA in the catholyte medium redirected the carbon flux towards carotenoid biosynthesis during mCO2ER. The faradaic efficiency of mCO2ER with MEA for carotenoid production was 4.5-fold higher than that of the control condition. These results suggest the mass transport bottleneck in bioelectrochemical systems could be effectively addressed by MEA-assissted mCO2ER, enabling highly efficient production of valuable products from CO2.

Co-sensitization of Copper Indium Gallium Disulfide and Indium Sulfide on Zinc Oxide Nanostructures: Effect of Morphology in Electrochemical Carbon Dioxide Reduction

Recent advances in nanoparticle materials can facilitate the electro-reduction of carbon dioxide (CO2) to form valuable products with high selectivity. Copper (Cu)-based electrodes are promising candidates to drive efficient and selective CO2 reduction. However, the application of Cu-based chalcopyrite semiconductors in the electrocatalytic reduction of CO2 is still limited. This study demonstrated that novel zinc oxide (ZnO)/copper indium gallium sulfide (CIGS)/indium sulfide (InS) heterojunction electrodes could be used in effective CO2 reduction for formic acid production. It has been determined that Faradaic efficiencies for formic acid production using ZnO nanowire (NW) and nanoflower (NF) structures vary due to structural and morphological differences. A ZnO NW/CIGS/InS heterojunction electrode resulted in the highest efficiency of 77.2% and 0.35 mA cm-2 of current density at a -0.24 V (vs. reversible hydrogen electrode) bias potential. Adding a ZTO intermediate layer by the spray pyrolysis method decreased the yield of formic acid and increased the yield of H2. Our work offers a new heterojunction electrode for efficient formic acid production via cost-effective and scalable CO2 reduction.

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.

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.

Enhancing the electrocatalytic performance of SnX2 (X = S and Se) monolayers for CO2 reduction to HCOOH via transition metal atom adsorption: a theoretical investigation

Exploring highly efficient, stable, and low-cost electrocatalysts for CO2 reduction reaction (CRR) can not only mitigate greenhouse gas emission but also store renewable energy. Herein, CO2 electroreduction to HCOOH on the surface of SnX2 (X = S and Se) monolayer-supported non-noble metal atoms (Fe, Co and Ni) was systematically investigated using first-principles calculations. Our results show that Fe, Co and Ni adsorbed on the surface of SnX2 (X = S and Se) monolayers can effectively enhance their electrocatalytic activity for CO2 reduction to HCOOH with low limiting potentials due to the decreasing energy barrier of *OOCH. Moreover, the lower free energy of the *OOCH intermediate on the surface of TM/SnX2 (X = S and Se) monolayers verifies that the electroreduction of CO2 to HCOOH prefers to proceed along the path: CO2 → *OOCH → *HCOOH → HCOOH. Interestingly, SnX2 (X = S and Se) monolayer-supported Co and Ni atoms prefer the HCOOH product with low CRR overpotentials of 0.03/0.01 V and 0.13/0.05 V, respectively, showing remarkable catalytic performance. This work reveals an efficient strategy to enhance the electrocatalytic performance of SnX2 (X = S and Se) monolayers for CO2 reduction to HCOOH, which could provide a way to design and develop new CRR catalysts experimentally in future.

In-modified Sn-MOFs with high catalytic performance in formate electrosynthesis from aqueous carbon dioxide

Electrochemical reduction of carbon dioxide (CO2ER) has become an effective solution to relieve the energy crisis and tackle climate change. In this study, a series of tin-based organic frameworks modified by In (Sn-MOF/Inx) were successfully synthesized via a simple hydrothermal method and explored for high formate-selective CO2ER. The pure Sn-MOF exhibits maximum formate selectivity with a faradaic efficiency (FEformate) of approximately 85.0% and a current density of 15 mA cm-2 at -1.16 VRHE, while the In (6%)-modified Sn-MOF (Sn-MOF/In6) delivers a much higher maximum FEformate (around 97.5%) and a current density of 16 mA cm-2 at -0.96 VRHE. Remarkably, the Sn-MOF/In6 exhibits a significantly larger specific surface area (183.3 m2 g-1) compared to the Sn-MOF (65.2 m2 g-1). These findings indicate that introducing In, an alien element with a slightly different outer orbital electron number from that of Sn, can significantly boost the selectivity and activity for CO2ER to formate. This study presents an efficient way to modify MOF catalysts through a well-designed introducing process.

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.

Self-Supporting Bi-Sb Bimetallic Nanoleaf for Electrochemical Synthesis of Formate by Highly Selective CO2 Reduction

Electrocatalytic reduction of CO₂ into valuable fuels and chemical feedstocks in a sustainable and environmentally friendly manner is an ideal way to mitigate climate change and environmental problems. Here, we fabricated a series of self-supporting Bi-Sb bimetallic nanoleaves on carbon paper (CP) by a facile electrodeposition method. The synergistic effect of Bi and Sb components and the change of the electronic structure lead to high formate selectivity and excellent stability in the electrochemical CO₂ reduction reaction (CO₂RR). Specifically, the Bi-Sb/CP bimetallic electrode achieved a high Faradic efficiency (FE_formate, 88.30%) at -0.9 V (vs RHE). The FE of formate remained above 80% in a broad potential range of -0.9 to -1.3 V (vs RHE), while FE_CO was suppressed below 6%. Density functional theory calculations showed that Bi(012)-Sb reduced the adsorption energy of the *OCHO intermediate and promoted the mass transfer of charges. The optimally adsorbed *OCHO intermediate promoted formate production while inhibiting the CO product pathway, thereby enhancing the selectivity to formate synthesis. Moreover, the CO₂RR performance was also investigated in a flow-cell system to evaluate its potential for industrial applications. The bimetallic Bi-Sb catalyst can maintain a steady current density of 160 mA/cm² at -1.2 V (vs RHE) for 25 h continuous electrolysis. Such excellent stability for formate generation in flow cells has rarely been reported in previous studies. This work offers new insights into the development of bimetallic self-supporting electrodes for CO₂ reduction.

A Tin Oxide-Coated Copper Foam Hybridized with a Gas Diffusion Electrode for Efficient CO2 Reduction to Formate with a Current Density Exceeding 1 A cm-2

The electrochemical CO₂ reduction reaction (CO₂ RR) is a promising strategy for closing the carbon cycle. Increasing the current density (  J) for CO₂ RR products is a critical requirement for the social implementation of this technology. Herein, nanoscale tin-oxide-modified copper-oxide foam is hybridized with a carbon-based gas-diffusion electrode (GDE). Using the resultant electrode, the J_formate is increased to -1152 mA cm^-2 at -1.2 V versus RHE in 1 m KOH, which is the highest value for CO₂ -to-formate electrolysis. The formate faradaic efficiency (FE_formate ) reaches ≈99% at -0.6 V versus RHE. The achievement of ultra-high-rate formate production is attributable to the following factors: i) homogeneously-modified Sn atoms suppressing H₂ evolution and ii) the hydrophobic carbon nanoparticles on GDEs penetrating the macroporous structure of the foam causing the increase in the thickness of triple-phase interface. Additionally, the FE_formate remains at ≈70% under a high J of -1.0 A cm^-2 for more than 20 h.

Recent progress of Bi-based electrocatalysts for electrocatalytic CO2 reduction

To mitigate excessively accumulated carbon dioxide (CO₂) in the atmosphere and tackle the associated environmental concerns, green and effective approaches are necessary. The electrocatalytic CO₂ reduction reaction (CO₂RR) using sustainable electricity under benign reaction conditions represents a viable way to produce value-added and profitable chemicals. In this minireview, recent studies regarding unary Bi electrocatalysts and binary BiSn electrocatalysts are symmetrically categorized and reviewed, as they disclose high faradaic efficiencies toward the production of formate/formic acid, which has a relatively higher value of up to 0.50 $·per kg and has been widely used in the chemical and pharmaceutical industry. In particular, the preparation methodologies, electrocatalyst morphologies, catalytic performances and the corresponding mechanisms are comprehensively presented. The use of solid-state electrolytes showing high economic prospects for directly obtaining high-purity formic acid is highlighted. Finally, the remaining questions and challenges for CO₂RR exploitations using Bi-related electrocatalysts are proposed, while perspectives and the corresponding strategies aiming to enhance their entire catalytic functionalities and boost their performance are provided.

Indium doped bismuth subcarbonate nanosheets for efficient electrochemical reduction of carbon dioxide to formate in a wide potential window

Electrochemical carbon dioxide (CO₂) reduction reaction (E-CO₂RR) to formate with high selectivity driven by renewable electricity is one of the most promising routes to carbon neutrality. Herein, we developed a novel indium (In)-doped bismuth subcarbonate (BOC) nanosheets (BOC-In-x NSs) through transformation of In-doped bismuth (Bi) nanoblocks (Bi-In-x NBs). The BOC-In-0.1 NSs achieved a maximum Faraday efficiency of formate (FE_formate) nearly 100% with high stability (22 h) and an appreciable average FE_formate of 93.5% in a wide potential window of 450 mV. The experimental and theoretical calculations indicate that the incorporation of In into BOC nanosheets enhanced the adsorption of CO₂ and the intermediates during the process of E-CO₂RR, and reduced the energy barrier for the formation of formate.

Roughness Effect of Cu on Electrocatalytic CO2 Reduction towards C2H4

Electrochemical reduction of CO 2 to produce valuable multi-carbon products is a promising avenue for promoting CO 2 conversion and achieving renewable energy storage, and it has also attracted considerable attention recently. However, the synthesis of Cu electrode with a controllable electrochemical active surface area (ECSA) to understand its role in CO 2 reduction to C 2 H 4 remains challenging. Herein, a series of Cu electrodes with different ECSA is synthesized through a simple oxidation-reduction approach. We reveal that the improved selectivity of C 2 H 4 is proportional to the ECSA of Cu in the low ECSA range, and a further increase in ECSA has a negligible effect on its selectivity. The enlarged surface area could strengthen the local pH effect near the surface of Cu electrode and suppress the generation of C 1 products as well as H 2 . The study provides a feasible strategy to rationally design electrocatalysts with high electrochemical CO 2 reduction performances.

Surface oxygen vacancies formation on Zn2SnO4 for bisphenol-A degradation under visible light: The tuning effect by peroxymonosulfate

Visible light catalysis has been widely coupled with persulfate activation for refractory pollutants removal, while the exact role of persulfate played in such composite system is still questionable. In this work, the relation between peroxymonosulfate (PMS) induced structure change and visible light responsive activity of inverse spinel: i.e., Zn₂SnO₄, was deciphered. Under the visible light illumination (λ> 420nm) PMS addition would endow the composite system with pollutant removal performance. Batch test revealed that 60% of bisphenol-A (5 mg L^-1) was mineralized within 3 h reaction time, by dosing 0.81 mM PMS and 0.1 g L^-1 catalyst. The above oxidative system was also effective for other refractory pollutants elimination. Further analysis indicated that PMS could reduce the band gap of spinel from 2.75 to 2.52 eV and thereby enabling its visible light activity. Photogenerated h⁺ induced •OH and e^- mediated •O₂^- contributed to the pollutant removal while h⁺ played a leading role. Density functional theory revealed that PMS would capture oxygen atom of spinel and induce surface oxygen vacancy defect structure formation. Also, three-oxygen atom coordinated Zn was identified as the possible catalyze site. This work is valuable for deep understanding the exact role of persulfate in photocatalytic system.

ZnSn nanocatalyst: Ultra-high formate selectivity from CO2 electrochemical reduction and the structure evolution effect

The introduction of tin (Sn) into Zn-based catalyst can change its intrinsic properties of the electrochemically reduction of CO₂ to CO, obtaining a high formate yield. The electron transfer from Zn to Sn lowers down the d-band center of Sn, leading to a more reliable surface adsorption of the *OCHO intermediate and high formate selectivity. The obtained ZnSn catalyst enables formate formation with a drastically boosted Faradaic efficiency (FE) up to 94%, which is 2.04 and 1.34 times of pure Zn and Sn foils, respectively, indicating a synergistic effect between Zn and Sn. During the electrochemical CO₂ reduction reaction (eCO₂RR) process, the morphology of the ZnSn catalyst evolved from nanoparticles to nanosheets, nanoneedles and collapsed structures, corresponding to the activation, stabilization and decay stages, respectively. This study provides a facile and controllable approach for the construction of novel bimetallic catalyst favoring formate selectivity based on the synergistic effect.

P-block atom modified Sn(200) surface as a promising electrocatalyst for two-electron CO2 reduction: a first-principles study

The P-block atom can effectively regulate the activity of two-electron CO2 reduction on Sn(200) surface.

SrO-layer insertion in Ruddlesden–Popper Sn-based perovskite enables efficient CO2 electroreduction towards formate

Tin (Sn)-based oxides have been proved to be promising catalysts for the electrochemical CO₂ reduction reaction (CO₂RR) to formate (HCOO⁻). However, their performance is limited by their reductive transformation into metallic derivatives during the cathodic reaction. This paper describes the catalytic chemistry of a Sr₂SnO₄ electrocatalyst with a Ruddlesden–Popper (RP) perovskite structure for the CO₂RR. The Sr₂SnO₄ electrocatalyst exhibits a faradaic efficiency of 83.7% for HCOO⁻ at −1.08 V vs. the reversible hydrogen electrode with stability for over 24 h. The insertion of the SrO-layer in the RP structure of Sr₂SnO₄ leads to a change in the filling status of the anti-bonding orbitals of the Sn active sites, which optimizes the binding energy of *OCHO and results in high selectivity for HCOO⁻. At the same time, the interlayer interaction between interfacial octahedral layers and the SrO-layers makes the crystalline structure stable during the CO₂RR. This study would provide fundamental guidelines for the exploration of perovskite-based electrocatalysts to achieve consistently high selectivity in the CO₂RR.

This paper describes how the insertion of a SrO-layer in Ruddlesden–Popper Sr₂SnO₄ perovskite electrocatalysts promotes CO₂ reduction towards formate via *OCHO intermediate. A faradaic efficiency of 83.7% and stability for over 24 h were obtained.

A gradient Sn4+@Sn2+ core@shell structure induced by a strong metal oxide–support interaction for enhanced CO2 electroreduction

A gradient Sn4+@Sn2+ core@shell structure induced by a strong tin oxide–g-C3N4 support interaction enhanced the adsorption and stabilization of CO2˙−, and hence the CO2RR performances.

Regulation of electrocatalytic activity by local microstructure: focusing on catalytic active zone

Traditional regulation methods of active sites have been successfully optimized the performance of electrocatalysts, but seem unable to achieve further breakthrough in the catalytic activity. Unlike the conventional viewpoint of focusing on single active site, the concept of local microstructure active zone is more comprehensive and new suits of methods to regulate reaction zone for electrocatalytic reactions are developed accordingly. The local microstructure active zone refers to the zone with high catalytic activity formed by the interaction between active atoms and neighboring coordination atoms as well as the surrounding environment. Instead of the traditional single active atom site, the active zone is more suitable for the actual electrochemical reaction process. According to this concept, the activity of the electrocatalysts can be coordinated by multiple active atoms. This strategy is beneficial to understand the relationship between material, structure and catalysis, which realizes the scientific design and synthesis of high performance electrocatalysts. This review provides the research progress of this strategy in electrocatalytic reactions, with the emphasis on their important applications in oxygen evolution reaction, urea oxidation reaction and carbon dioxide reduction.

Electronic Tuning of SnS2 Nanosheets by Hydrogen Incorporation for Efficient CO2 Electroreduction

Surface functionalization with atoms serves as an important strategy to modulate the catalytic activities of low-dimensional nanomaterials. Herein, we developed a facile hydrogen incorporation strategy for improving the catalytic activities of SnS₂ nanosheets toward CO₂ electroreduction. Compared with SnS₂ nanosheets, the hydrogen-incorporated SnS₂ (denoted as H-SnS₂) nanosheets exhibited high current density and Faradaic efficiency (FE) for formate. At -0.9 V vs RHE, H-SnS₂ nanosheets displayed a maximum FE of 93% for carbonaceous product, which rivals the activities of most Sn-based catalysts in CO₂ electroreduction. Mechanistic studies disclosed that the incorporation of surface hydrogen induced the electron injection into the structures of H-SnS₂ nanosheets, which largely facilitates the process of CO₂ activation. Density functional theory (DFT) calculations further revealed that hydrogen incorporation decreased the energy barrier for the formation of HCOO* intermediates, thus contributing to the CO₂-to-formate conversion on H-SnS₂ nanosheets.

Electrochemical Reduction of CO2 at Coinage Metal Nanodendrites in Aqueous Ethanolamine

Electrocatalytic reduction of CO₂ into usable chemicals is a promising path to address climate change and energy challenges. Herein, we demonstrate the synthesis of unique coinage metal (Cu, Ag, and Au) nanodendrites (NDs) via a facile galvanic replacement reaction (GRR), which can be effective electrocatalysts for the reduction of CO₂ in an ethanolamine (EA) solution. Each metal ND surface was directly grown on glassy-carbon (GC) substrates from a mixture of Zn dust and the respective precursor solution. The electrocatalytic activities of the synthesized ND surfaces were optimized for CO₂ reduction in EA solution by varying their composition. It was determined that a 0.05 mol fraction of EA exhibited the highest catalytic activity for all metal NDs. Linear sweep voltammetry (LSV) and electrochemical impedance spectroscopy (EIS) techniques showed that metal-ND electrodes possessed higher current densities, lower onset potentials and lower charge-transfer resistances for CO₂ reduction than their smooth polycrystalline electrode counterparts, indicating improved CO₂ reduction catalytic activity. It was determined, using FTIR and NMR spectroscopy, that formate was produced as a result of the CO₂ reduction.