Enhancing Activity and Reducing Cost for Electrochemical Reduction of CO2 by Supporting Palladium on Metal Carbides

Electrochemical CO₂ reduction reaction (CO₂RR) with renewable electricity is a potentially sustainable method to reduce CO₂ emissions. Palladium supported on cost‐effective transition‐metal carbides (TMCs) are studied to reduce the Pd usage and tune the activity and selectivity of the CO₂RR to produce synthesis gas, using a combined approach of studying thin films and practical powder catalysts, in situ characterization, and density functional theory (DFT) calculations. Notably, Pd/TaC exhibits higher CO₂RR activity, stability and CO Faradaic efficiency than those of commercial Pd/C while significantly reducing the Pd loading. In situ measurements confirm the transformation of Pd into hydride (PdH) under the CO₂RR environment. DFT calculations reveal that the TMC substrates modify the binding energies of key intermediates on supported PdH. This work suggests the prospect of using TMCs as low‐cost and stable substrates to support and modify Pd for enhanced CO₂RR activity.     

Electrochemical Conversion of CO2 to Syngas with Controllable CO/H2 Ratios over Co and Ni Single‐Atom Catalysts

The electrochemical CO₂ reduction reaction (CO₂RR) to yield synthesis gas (syngas, CO and H₂) has been considered as a promising method to realize the net reduction in CO₂ emission. However, it is challenging to balance the CO₂RR activity and the CO/H₂ ratio. To address this issue, nitrogen‐doped carbon supported single‐atom catalysts are designed as electrocatalysts to produce syngas from CO₂RR. While Co and Ni single‐atom catalysts are selective in producing H₂ and CO, respectively, electrocatalysts containing both Co and Ni show a high syngas evolution (total current >74 mA cm^?2) with CO/H₂ ratios (0.23–2.26) that are suitable for typical downstream thermochemical reactions. Density functional theory calculations provide insights into the key intermediates on Co and Ni single‐atom configurations for the H₂ and CO evolution. The results present a useful case on how non‐precious transition metal species can maintain high CO₂RR activity with tunable CO/H₂ ratios.     

Electrochemical Conversion of CO2 to Syngas with Controllable CO/H2 Ratios over Co and Ni Single-Atom Catalysts

The electrochemical CO₂ reduction reaction (CO₂RR) to yield synthesis gas (syngas, CO and H₂) has been considered as a promising method to realize the net reduction in CO₂ emission. However, it is challenging to balance the CO₂RR activity and the CO/H₂ ratio. To address this issue, nitrogen-doped carbon supported single-atom catalysts are designed as electrocatalysts to produce syngas from CO₂RR. While Co and Ni single-atom catalysts are selective in producing H₂ and CO, respectively, electrocatalysts containing both Co and Ni show a high syngas evolution (total current >74 mA cm⁻²) with CO/H₂ ratios (0.23–2.26) that are suitable for typical downstream thermochemical reactions. Density functional theory calculations provide insights into the key intermediates on Co and Ni single-atom configurations for the H₂ and CO evolution. The results present a useful case on how non-precious transition metal species can maintain high CO₂RR activity with tunable CO/H₂ ratios.     

Metal‐Doped Nitrogenated Carbon as an Efficient Catalyst for Direct CO2 Electroreduction to CO and Hydrocarbons

This study explores the kinetics, mechanism, and active sites of the CO₂ electroreduction reaction (CO2RR) to syngas and hydrocarbons on a class of functionalized solid carbon‐based catalysts. Commercial carbon blacks were functionalized with nitrogen and Fe and/or Mn ions using pyrolysis and acid leaching. The resulting solid powder catalysts were found to be active and highly CO selective electrocatalysts in the electroreduction of CO₂ to CO/H₂ mixtures outperforming a low‐area polycrystalline gold benchmark. Unspecific with respect to the nature of the metal, CO production is believed to occur on nitrogen functionalities in competition with hydrogen evolution. Evidence is provided that sufficiently strong interaction between CO and the metal enables the protonation of CO and the formation of hydrocarbons. Our results highlight a promising new class of low‐cost, abundant electrocatalysts for synthetic fuel production from CO₂.     

Highly Efficient CO2 Electroreduction on ZnN4‐based Single‐Atom Catalyst

The electrochemical reduction reaction of carbon dioxide (CO2RR) to carbon monoxide (CO) is the basis for the further synthesis of more complex carbon‐based fuels or attractive feedstock. Single‐atom catalysts have unique electronic and geometric structures with respect to their bulk counterparts, thus exhibiting unexpected catalytic activities. A nitrogen‐anchored Zn single‐atom catalyst is presented for CO formation from CO2RR with high catalytic activity (onset overpotential down to 24 mV), high selectivity (Faradaic efficiency for CO (FE_CO) up to 95 % at ?0.43 V), remarkable durability (>75 h without decay of FE_CO), and large turnover frequency (TOF, up to 9969 h^?1). Further experimental and DFT results indicate that the four‐nitrogen‐anchored Zn single atom (Zn‐N₄) is the main active site for CO2RR with low free energy barrier for the formation of *COOH as the rate‐limiting step.     

Designs of Tandem Catalysts and Cascade Catalytic Systems for CO2 Upgrading

Upgrading CO₂ into multi-carbon (C2+) compounds through the CO₂ reduction reaction (CO₂RR) offers a practical approach to mitigate atmospheric CO₂ while simultaneously producing high value chemicals. The reaction pathways for C2+ production involve multi-step proton-coupled electron transfer (PCET) and C−C coupling processes. By increasing the surface coverage of adsorbed protons (*H_ad) and *CO intermediates, the reaction kinetics of PCET and C−C coupling can be accelerated, thereby promoting C2+ production. However, *H_ad and *CO are competitively adsorbed intermediates on monocomponent catalysts, making it difficult to break the linear scaling relationship between the adsorption energies of the *H_ad/*CO intermediate. Recently, tandem catalysts consisting of multicomponents have been developed to improve the surface coverage of *H_ad or *CO by enhancing water dissociation or CO₂-to-CO production on auxiliary sites. In this context, we provide a comprehensive overview of the design principles of tandem catalysts based on reaction pathways for C2+ products. Moreover, the development of cascade CO₂RR catalytic systems that integrate CO₂RR with downstream catalysis has expanded the range of potential CO₂ upgrading products. Therefore, we also discuss recent advancements in cascade CO₂RR catalytic systems, highlighting the challenges and perspectives in these systems.     

Molecular Evidence for Metallic Cobalt Boosting CO2 Electroreduction on Pyridinic Nitrogen

Nitrogen‐doped carbon materials (N‐C_mat) are emerging as low‐cost metal‐free electrocatalysts for the electrochemical CO₂ reduction reaction (CO₂RR), although the activities are still unsatisfactory and the genuine active site is still under debate. We demonstrate that the CO₂RR to CO preferentially takes place on pyridinic N rather than pyrrolic N using phthalocyanine (Pc) and porphyrin with well‐defined N‐C_mat configurations as molecular model catalysts. Systematic experiments and theoretic calculations further reveal that the CO₂RR performance on pyridinic N can be significantly boosted by electronic modulation from in‐situ‐generated metallic Co nanoparticles. By introducing Co nanoparticles, Co@Pc/C can achieve a Faradaic efficiency of 84 % and CO current density of 28 mA cm^?2 at ?0.9 V, which are 18 and 47 times higher than Pc/C without Co, respectively. These findings provide new insights into the CO₂RR on N‐C_mat, which may guide the exploration of cost‐effective electrocatalysts for efficient CO₂ reduction.     

Tweaking Photo CO2 Reduction by Altering Lewis Acidic Sites in Metalated-Porous Organic Polymer for Adjustable H2/CO Ratio in Syngas Production

Herein, we have specifically designed two metalated porous organic polymers ( Zn-POP and Co-POP ) for syngas (CO+H₂) production from gaseous CO₂. The variable H₂/CO ratio of syngas with the highest efficiency was produced in water medium (without an organic hole scavenger and photosensitizer) by utilizing the basic principle of Lewis acid/base chemistry. Also, we observed the formation of entirely different major products during photocatalytic CO₂ reduction and water splitting with the help of the two catalysts, where CO (145.65 μmol g⁻¹ h⁻¹) and H₂ (434.7 μmol g⁻¹ h⁻¹) production were preferentially obtained over Co-POP & Zn-POP , respectively. The higher electron density/better Lewis basic nature of Co-POP was investigated further using XPS, XANES, and NH₃-TPD studies, which considerably improve CO₂ activation capacity. Moreover, the structure–activity relationship was confirmed via in situ DRIFTS and DFT studies, which demonstrated the formation of COOH* intermediate along with the thermodynamic feasibility of CO₂ reduction over Co-POP while water splitting occurred preferentially over Zn-POP .     

Efficient Electrosynthesis of Syngas with Tunable CO/H2 Ratios over ZnxCd1−xS‐Amine Inorganic–Organic Hybrids

Efficient electrochemical reduction of CO₂ and H₂O into industrial syngas with tunable CO/H₂ ratios, especially integrated with anodic organic synthesis to replace the low‐value oxygen evolution reaction (OER), is highly desirable. Here, integration of controllable partial substitution of zinc (Zn) with amine incorporation into CdS‐amine inorganic‐organic hybrids is used to generate highly efficient electrocatalysts for synthesizing syngas with tunable CO/H₂ ratios (0–19.7), which are important feedstocks for the Fischer–Tropsch process. Diethylenetriamine could enhance the adsorption and accelerate the activation of CO₂ to form the key intermediate COOH* for CO formation. Zn substitution promoted the hydrogen evolution reaction (HER), leading to tunable CO/H₂ ratios. Importantly, syngas and dihydroisoquinoline can be simultaneously synthesized by pairing with anodic semi‐oxidation of tetrahydroisoquinoline in a Zn_xCd_1?xS‐Amine ∥ Ni₂P two‐electrode electrolyzer.     

Enhancing CO2 Electroreduction to Methane with a Cobalt Phthalocyanine and Zinc–Nitrogen–Carbon Tandem Catalyst

Developing copper-free catalysts for CO₂ conversion into hydrocarbons and oxygenates is highly desirable for electrochemical CO₂ reduction reaction (CO₂RR). Herein, we report a cobalt phthalocyanine (CoPc) and zinc–nitrogen–carbon (Zn-N-C) tandem catalyst for CO₂RR to CH₄. This tandem catalyst shows a more than 100 times enhancement of the CH₄/CO production rate ratio compared with CoPc or Zn-N-C alone. Density functional theory (DFT) calculations and electrochemical CO reduction reaction results suggest that CO₂ is first reduced into CO over CoPc and then CO diffuses onto Zn-N-C for further conversion into CH₄ over Zn-N₄ site, decoupling complicated CO₂RR pathway on single active site into a two-step tandem reaction. Moreover, mechanistic analysis indicates that CoPc not only generates CO but also enhances the availability of *H over adjacent N sites in Zn-N₄, which is the key to achieve the high CH₄ production rate and understand the intriguing electrocatalytic behavior which is distinctive to copper-based tandem catalysts.     

Palladium Encapsulated by an Oxygen-Saturated TiO2 Overlayer for Low-Temperature SO2-Tolerant Catalysis during CO Oxidation

The development of oxidation catalysts that are resistant to sulfur poisoning is crucial for extending the lifespan of catalysts in real-working conditions. Herein, we describe the design and synthesis of oxide-metal interaction (OMI) catalyst under oxidative atmospheres. By using organic coated TiO₂, an oxide/metal inverse catalyst with non-classical oxygen-saturated TiO₂ overlayers were obtained at relatively low temperature. These catalysts were found to incorporate ultra-small Pd metal and support particles with exceptional reactivity and stability for CO oxidation (under 21 vol % O₂ and 10 vol % H₂O). In particular, the core (Pd)-shell (TiO₂) structured OMI catalyst exhibited excellent resistance to SO₂ poisoning, yielding robust CO oxidation performance at 120 °C for 240 h (at 100 ppm SO₂ and 10 vol % H₂O). The stability of this new OMI catalyst was explained through density functional theory (DFT) calculations that interfacial oxygen atoms at Pd−O−Ti sites (of oxygen-saturated overlayers) serve as non-metal active sites for low-temperature CO oxidation, and change the SO₂ adsorption from metal(d)-to-SO₂(π*) back-bonding to much weaker σ(Ti−S) bonding.     

Ultrathin two-dimensional triptycence-based metal-organic framework for highly selective CO2 electroreduction to CO

Efficient CO₂ reduction reaction (CO₂RR) is one of the important topics in energy and environment field, but improving the electrochemical selectivity of specific product is a great challenge. Herein, we reported a unprecedented two-dimensional (2D) metal?organic framework with CuO₄ unit (denoted as Cu-HHTT, HHTT = 9,10-dihydro-9,10-[1,2]benzenoanthracene-2,3,6,7,14,15-hexaol) as the electrocatalyst for CO₂RR. Cu-HHTT exhibits high performance for CO₂RR to produce CO, namely Faradaic efficiency of 96.6% toward CO with a current density of 18 mA/cm² at the potential of ?0.6 V vs. RHE. Density function theory reveals that the desorption of CO species exhibits a lower energy barrier than that of hydrogenation of *CO intermediate, resulting in CO as the main product instead of alcohols or hydrocarbons.     

Tuning C1/C2 Selectivity of CO2 Electrochemical Reduction over in-Situ Evolved CuO/SnO2 Heterostructure

Heterostructured oxides with versatile active sites, as a class of efficient catalysts for CO₂ electrochemical reduction (CO₂ER), are prone to undergo structure reconstruction under working conditions, thus bringing challenges to understanding the reaction mechanism and rationally designing catalysts. Herein, we for the first time elucidate the structural reconstruction of CuO/SnO₂ under electrochemical potentials and reveal the intrinsic relationship between CO₂ER product selectivity and the in situ evolved heterostructures. At −0.85 V_RHE, the CuO/SnO₂ evolves to Cu₂O/SnO₂ with high selectivity to HCOOH (Faradaic efficiency of 54.81 %). Mostly interestingly, it is reconstructed to Cu/SnO_2-x at −1.05 V_RHE with significantly improved Faradaic efficiency to ethanol of 39.8 %. In situ Raman spectra and density functional theory (DFT) calculations reveal that the synergetic absorption of *COOH and *CHOCO intermediates at the interface of Cu/SnO_2-x favors the formation of *CO and decreases the energy barrier of C−C coupling, leading to high selectivity to ethanol.     

Rational Design of Crystalline Covalent Organic Frameworks for Efficient CO2 Photoreduction with H2O

Solar energy‐driven conversion of CO₂ into fuels with H₂O as a sacrificial agent is a challenging research field in photosynthesis. Herein, a series of crystalline porphyrin‐tetrathiafulvalene covalent organic frameworks (COFs) are synthesized and used as photocatalysts for reducing CO₂ with H₂O, in the absence of additional photosensitizer, sacrificial agents, and noble metal co‐catalysts. The effective photogenerated electrons transfer from tetrathiafulvalene to porphyrin by covalent bonding, resulting in the separated electrons and holes, respectively, for CO₂ reduction and H₂O oxidation. By adjusting the band structures of TTCOFs, TTCOF‐Zn achieved the highest photocatalytic CO production of 12.33 μmol with circa 100 % selectivity, along with H₂O oxidation to O₂. Furthermore, DFT calculations combined with a crystal structure model confirmed the structure–function relationship. Our work provides a new sight for designing more efficient artificial crystalline photocatalysts.     

Effect of Halide Anions on the Electroreduction of CO2 to C2H4: A Density Functional Theory Study**

The halide anions present in the electrolyte improve the Faradaic efficiencies (FEs) of the multi-hydrocarbon (C₂₊) products for the electrochemical reduction of CO₂ over copper (Cu) catalysts. However, the mechanism behind the increased yield of C₂₊ products with the addition of halide anions remains indistinct. In this study, we analysed the mechanism by investigating the electronic structures and computing the relative free energies of intermediates formed from CO₂ to C₂H₄ on the Cu (100) facet based on density functional theory (DFT) calculations. The results show that formyl *CHO from the hydrogenation reaction of the adsorbed *CO acts as the key intermediate, and the C−C coupling reaction occurs preferentially between *CHO and *CO with the formation of a *CHO-CO intermediate. We then propose a free-energy pathway of C₂H₄ formation. We find that the presence of halide anions significantly decreases the free energy of the *CHOCH intermediate, and enhances desorption of C₂H₄ in the order of I⁻>Cl⁻>Br⁻>F⁻. Lastly, the obtained results are rationalized through Bader charge analysis.     

A Highly Selective Copper–Indium Bimetallic Electrocatalyst for the Electrochemical Reduction of Aqueous CO2 to CO

The challenge in the electrochemical reduction of aqueous carbon dioxide is in designing a highly selective, energy‐efficient, and non‐precious‐metal electrocatalyst that minimizes the competitive reduction of proton to form hydrogen during aqueous CO₂ conversion. A non‐noble metal electrocatalyst based on a copper‐indium (Cu‐In) alloy that selectively converts CO₂ to CO with a low overpotential is reported. The electrochemical deposition of In on rough Cu surfaces led to Cu‐In alloy surfaces. DFT calculations showed that the In preferentially located on the edge sites rather than on the corner or flat sites and that the d‐electron nature of Cu remained almost intact, but adsorption properties of neighboring Cu was perturbed by the presence of In. This preparation of non‐noble metal alloy electrodes for the reduction of CO₂ provides guidelines for further improving electrocatalysis.     

Metal‐Free Fluorine‐Doped Carbon Electrocatalyst for CO2 Reduction Outcompeting Hydrogen Evolution

The electrochemical CO₂ reduction (ECDRR), as a key reaction in artificial photosynthesis to implement renewable energy conversion/storage, has been inhibited by the low efficiency and high costs of the electrocatalysts. Herein, we synthesize a fluorine‐doped carbon (FC) catalyst by pyrolyzing commercial BP 2000 with a fluorine source, enabling a highly selective CO₂‐to‐CO conversion with a maximum Faradaic efficiency of 90 % at a low overpotential of 510 mV and a small Tafel slope of 81 mV dec^?1, outcompeting current metal‐free catalysts. Moreover, the higher partial current density of CO and lower partial current density of H₂ on FC relative to pristine carbon suggest an enhanced inherent activity towards ECDRR as well as a suppressed hydrogen evolution by fluorine doping. Fluorine doping activates the neighbor carbon atoms and facilitates the stabilization of the key intermediate COOH* on the fluorine‐doped carbon material, which are also blocked for competing hydrogen evolution, resulting in superior CO₂‐to‐CO conversion.     

Exclusive Formation of Formic Acid from CO2 Electroreduction by a Tunable Pd‐Sn Alloy

Conversion of carbon dioxide (CO₂) into fuels and chemicals by electroreduction has attracted significant interest, although it suffers from a large overpotential and low selectivity. A Pd‐Sn alloy electrocatalyst was developed for the exclusive conversion of CO₂ into formic acid in an aqueous solution. This catalyst showed a nearly perfect faradaic efficiency toward formic acid formation at the very low overpotential of −0.26 V, where both CO formation and hydrogen evolution were completely suppressed. Density functional theory (DFT) calculations suggested that the formation of the key reaction intermediate HCOO* as well as the product formic acid was the most favorable over the Pd‐Sn alloy catalyst surface with an atomic composition of PdSnO₂, consistent with experiments.     

Isolated Tin(IV) Active Sites for Highly Efficient Electroreduction of CO2 to CH4 in Neutral Aqueous Solution

The development of efficient electrocatalysts with non-copper metal sites for electrochemical CO₂ reduction reactions (eCO₂RR) to hydrocarbons and oxygenates is highly desirable, but still a great challenge. Herein, a stable metal–organic framework (DMA)₄[Sn₂(THO)₂] (Sn-THO, THO⁶⁻ = triphenylene-2,3,6,7,10,11-hexakis(olate), DMA = dimethylammonium) with isolated and distorted octahedral SnO₆²⁻ active sites is reported as an electrocatalyst for eCO₂RR, showing an exceptional performance for eCO₂RR to the CH₄ product rather than the common products formate and CO for reported Sn-based catalysts. The partial current density of CH₄ reaches a high value of 34.5 mA cm⁻², surpassing most reported copper-based and all non-Cu metal-based catalysts. Our experimental and theoretical results revealed that the isolated SnO₆²⁻ active site favors the formation of key *OCOH species to produce CH₄ and can greatly inhibit the formation of *OCHO and *COOH species to produce *HCOOH and *CO, respectively.     

Selective CO2 Reduction to Ethylene Mediated by Adaptive Small-molecule Engineering of Copper-based Electrocatalysts

Electrochemical CO₂ reduction reaction (CO₂RR) over Cu catalysts exhibits enormous potential for efficiently converting CO₂ to ethylene (C₂H₄). However, achieving high C₂H₄ selectivity remains a considerable challenge due to the propensity of Cu catalysts to undergo structural reconstruction during CO₂RR. Herein, we report an in situ molecule modification strategy that involves tannic acid (TA) molecules adaptive regulating the reconstruction of a Cu-based material to a pathway that facilitates CO₂ reduction to C₂H₄ products. An excellent Faraday efficiency (FE) of 63.6 % on C₂H₄ with a current density of 497.2 mA cm⁻² in flow cell was achieved, about 6.5 times higher than the pristine Cu catalyst which mainly produce CH₄. The in situ X-ray absorption spectroscopy and Raman studies reveal that the hydroxyl group in TA stabilizes Cu^δ+ during the CO₂RR. Furthermore, theoretical calculations demonstrate that the Cu^δ+/Cu⁰ interfaces lower the activation energy barrier for *CO dimerization, and hydroxyl species stabilize the *COH intermediate via hydrogen bonding, thereby promoting C₂H₄ production. Such molecule engineering modulated electronic structure provides a promising strategy to achieve highly selective CO₂ reduction to value-added chemicals.