COOH Intermediates Research Articles

Three-Phase-Heterojunction Cu/Cu2O-Sb2O3 Catalyst Enables Efficient CO2 Electroreduction to CO and High-Performance Aqueous Zn-CO2 Battery.

Zn-CO2 batteries are excellent candidates for both electrical energy output and CO2 utilization, whereas the main challenge is to design electrocatalysts for electrocatalytic CO2 reduction reactions with high selectivity and low cost. Herein, the three-phase heterojunction Cu-based electrocatalyst (Cu/Cu2O-Sb2O3-15) is synthesized and evaluated for highly selective CO2 reduction to CO, which shows the highest faradaic efficiency of 96.3% at -1.3 V versus reversible hydrogen electrode, exceeding the previously reported best values for Cu-based materials. In situ spectroscopy and theoretical analysis indicate that the Sb incorporation into the three-phase heterojunction Cu/Cu2O-Sb2O3-15 nanomaterial promotes the formation of key *COOH intermediates compared with the normal Cu/Cu2O composites. Furthermore, the rechargeable aqueous Zn-CO2 battery assembled with Cu/Cu2O-Sb2O3-15 as the cathode harvests a peak power density of 3.01 mW cm-2 as well as outstanding cycling stability of 417 cycles. This research provides fresh perspectives for designing advanced cathodic electrocatalysts for rechargeable Zn-CO2 batteries with high-efficient electricity output together with CO2 utilization.

Light‐Driven C−C Coupling for Targeted Synthesis of CH3COOH with Nearly 100 % Selectivity from CO2

AbstractTargeted synthesis of acetic acid (CH3COOH) from CO2 photoreduction under mild conditions mainly limits by the kinetic challenge of the C−C coupling. Herein, we utilized doping engineering to build charge‐asymmetrical metal pair sites for boosted C−C coupling, enhancing the activity and selectivity of CO2 photoreduction towards CH3COOH. As a prototype, the Pd doped Co3O4 atomic layers are synthesized, where the established charge‐asymmetrical cobalt pair sites are verified by X‐ray photoelectron spectroscopy and X‐ray absorption near edge spectroscopy spectra. Theoretical calculations not only reveal the charge‐asymmetrical cobalt pair sites caused by Pd atom doping, but also manifest the promoted C−C coupling of double *COOH intermediates through shortening of the coupled C−C bond distance from 1.54 to 1.52 Å and lowering their formation energy barrier from 0.77 to 0.33 eV. Importantly, the decreased reaction energy barrier from the protonation of two*COOH into *CO intermediates for the Pd‐Co3O4 atomic layer slab is 0.49 eV, higher than that of the Co3O4 atomic layer slab (0.41 eV). Therefore, the Pd‐Co3O4 atomic layers exhibit the CH3COOH evolution rate of ca. 13.8 μmol g−1 h−1 with near 100% selectivity, both of which outperform all previously reported single photocatalysts for CO2 photoreduction towards CH3COOH under similar conditions.

Light-Driven C-C Coupling for Targeted Synthesis of CH3 COOH with Nearly 100 % Selectivity from CO2.

Targeted synthesis of acetic acid (CH3 COOH) from CO2 photoreduction under mild conditions mainly limits by the kinetic challenge of the C-C coupling. Herein, we utilized doping engineering to build charge-asymmetrical metal pair sites for boosted C-C coupling, enhancing the activity and selectivity of CO2 photoreduction towards CH3 COOH. As a prototype, the Pd doped Co3 O4 atomic layers are synthesized, where the established charge-asymmetrical cobalt pair sites are verified by X-ray photoelectron spectroscopy and X-ray absorption near edge spectroscopy spectra. Theoretical calculations not only reveal the charge-asymmetrical cobalt pair sites caused by Pd atom doping, but also manifest the promoted C-C coupling of double *COOH intermediates through shortening of the coupled C-C bond distance from 1.54 to 1.52 Å and lowering their formation energy barrier from 0.77 to 0.33 eV. Importantly, the decreased reaction energy barrier from the protonation of two*COOH into *CO intermediates for the Pd-Co3 O4 atomic layer slab is 0.49 eV, higher than that of the Co3 O4 atomic layer slab (0.41 eV). Therefore, the Pd-Co3 O4 atomic layers exhibit the CH3 COOH evolution rate of ca. 13.8 μmol g-1 h-1 with near 100% selectivity, both of which outperform all previously reported single photocatalysts for CO2 photoreduction towards CH3 COOH under similar conditions.

Confined bismuth single atoms and nanoparticles dual-sites constructed via reverse etching for CO2 photoreduction to CH4

Synchronizing the directional photogenerated transfer of electrons and regulating the CO2 photocatalytic reduction process are key to achieving the efficient and highly selective photocatalytic reduction of CO2. The design of highly-dispersed active sites and the efficient collaboration of multiple sites are of great importance in attaining the above target. Herein, a reverse etching route was first proposed to confine Bi single atoms and nanoparticles as dual-sites for assisting CO2 photoreduction on TiO2, avoiding the mutual masking of the active sites. The Synergism of the dual-sites achieves the hydrodeoxygenation of * COOH and ushers the directional conversion of CO2 to CH4. Highly dispersed single Bi atoms could induce the transfer of photogenerated electrons, enhance CO2 absorption, and further provide active sites for reducing CO2 to *COOH intermediates. Besides, appropriate Bi nanoparticles could promote the separation and transfer of photogenerated and inhibit the formation of hydroxyl groups; more importantly, they could promote the release of protons, which would further accelerate the conversion of *COOH to CH4. After being integrated, the optimized dual-Bi/TiO2 catalyst achieves a CH4 generation rate of 103.89 μmol·g−1·h−1 with an impressive selectivity of 96.87 % as well as remarkable durability for photocatalytic CO2 reduction. This work provides new insights into developing robust catalysts through the artful design of synergistic catalytic sites for efficient photocatalytic CO2 conversion.

Easily constructed porous silver films for efficient catalytic CO2 reduction and Zn-CO2 batteries.

For the electroreduction of carbon dioxide into high value-added chemicals, highly active and selective catalysts are crucial, and metallic silver is one of the most intriguing candidate materials available at a reasonable cost. Herein, through a novel two-step operation of Ag paste/SBA-15 coating and HF etching, porous silver films on a commercial carbon paper with a waterproofer (p-Ag/CP) could be easily fabricated on a large scale as highly efficient carbon dioxide reduction reaction (CO2RR) electrocatalysts with a CO Faraday efficiency (FECO) as high as 96.7% at -1.0 V vs. the reversible hydrogen electrode (RHE), and it still reaches up to 90% FECO over applied potentials ranging from -0.8 to -1.1 V vs. the RHE. Meanwhile, the membrane electrode assembly (MEA) utilizing the p-Ag/CP catalyst has achieved a current density, FECO, and stability of ∼60 mA cm-2, >91%, and 11 h, respectively. Furthermore, the assembled aqueous Zn-CO2 battery using p-Ag/CP cathode yielded a peak power density of 0.34 mW cm-2, 75 charge-discharge cycles for 25 h, and 64% FECO at 2.5 mA cm-2. Compared with flat Ag/CP, the significant enhancement in the CO2RR activity of p-Ag/CP was mainly attributed to the distinctive porous structure and an improved three-phase boundary, which is capable of inducing the stabilization of *COOH intermediates, increased active specific surface areas, fast electron transfer kinetic and mass transportation. Further, theoretical calculations revealed that p-Ag/CP possessed an optimized energy barrier for *COOH intermediates.

Revealing the synergistic effect of Ni single atoms and adjacent 3d metal doped Ni nanoparticles in electrocatalytic CO2 reduction.

Herein, we report the successful fabrication of a series of transition metal doped Ni nanoparticles (NPs) coordinated with Ni single atoms in nitrogen-doped carbon nanotubes (denoted as Ni1+NPsM-NCNTs, M = Mn, Fe, Co, Cu and Zn; Ni1 = Ni single atom). X-ray absorption fine structure reveals the coexistence of Ni single atoms with Ni-N4 coordination and NiM NPs. When applied for electrocatalytic CO2RR, the Ni1+NPsM-NCNT compounds show the Faradaic efficiency of CO (FECO) with a volcano-like tendency of Mn < Fe ≈ Co < Zn < Cu, in which the Ni1+NPsCu-NCNT exhibits the highest FECO of 96.92%, a current density of 171.25 mA cm-2 and a sustainable stability over 24 hours at a current density of 100 mA cm-2, outperforming most reported examples in the literature. Detailed experiments and theoretical calculations reveal that for Ni1+NPsCu-NCNTs, the electron transfer from NiCu NPs to Ni single atoms strengthens the adsorption of *COOH intermediates. Moreover, the d-band center of Ni-N in Ni1+NPsCu-NCNT is upshifted, providing stronger binding with the reaction intermediates of *COOH, whereas the NiCu NPs increase the Gibbs free energy change of the Volmer step, suppressing the competitive HER.

Ag/ZnO Composite Structure Modulated by Hybrid Engineering for Efficient Electroreduction of CO2 to CO

AbstractElectrochemical carbon dioxide reduction reaction (ECO2RR) act as a green and value‐added technology, which could convert CO2 into products with circulation value, has a good application prospect. However, the activity of non‐mainstream Zn‐based catalysts has not yet reached satisfactory expectations, and how to further modify them to improve the performance of CO production performance still remains a challenge. In our work, a design of hybrid engineering is proposed to enhance the activity of Zn‐based materials, in which the introduction of slight Ag could not only optimize the electronic structure of Zn‐based materials but also effectively increase their electrochemically active surface area. Compared with pure ZnO, the faraday efficiency of CO (FECO) in Ag/ZnO increased by 1.7 times from 45.9 % to 80.3 % at −0.977 V vs. RHE. Moreover, the long‐term and stable output of products in the electrolysis process also confirms the superior stability of the hybrid catalyst According to the in‐situ Raman study, it is confirmed that the main factor for the enhanced CO selectivity after the introduction of Ag is the improvement of the key *COOH intermediates. This study provides an effective strategy for constructing highly active Zn‐based catalysts for industrial‐scale ECO2RR.

Stabilizing Undercoordinated Zn Active Sites through Confinement in CeO2 Nanotubes for Efficient Electrochemical CO2 Reduction.

Zn-based catalysts hold great potential to replace the noble metal-based ones for CO2 reduction reaction (CO2 RR). Undercoordinated Zn (Znδ+ ) sites may serve as the active sites for enhanced CO production by optimizing the binding energy of *COOH intermediates. However, there is relatively less exploration into the dynamic evolution and stability of Znδ+ sites during CO2 reduction process. Herein, we present ZnO, Znδ+ /ZnO and Zn as catalysts by varying the applied reduction potential. Theoretical studies reveal that Znδ+ sites could suppress HER and HCOOH production to induce CO generation. And Znδ+ /ZnO presents the highest CO selectivity (FECO 70.9 % at -1.48 V vs. RHE) compared to Zn and ZnO. Furthermore, we propose a CeO2 nanotube with confinement effect and Ce3+ /Ce4+ redox to stabilize Znδ+ species. The hollow core-shell structure of the Znδ+ /ZnO/CeO2 catalyst enables to extremely expose electrochemically active area while maintaining the Znδ+ sites with long-time stability. Certainly, the target catalyst affords a FECO of 76.9 % at -1.08 V vs. RHE and no significant decay of CO selectivity in excess of 18 h.

Stabilizing Undercoordinated Zn Active Sites through Confinement in CeO2 Nanotubes for Efficient Electrochemical CO2 Reduction

AbstractZn‐based catalysts hold great potential to replace the noble metal‐based ones for CO2 reduction reaction (CO2RR). Undercoordinated Zn (Znδ+) sites may serve as the active sites for enhanced CO production by optimizing the binding energy of *COOH intermediates. However, there is relatively less exploration into the dynamic evolution and stability of Znδ+ sites during CO2 reduction process. Herein, we present ZnO, Znδ+/ZnO and Zn as catalysts by varying the applied reduction potential. Theoretical studies reveal that Znδ+ sites could suppress HER and HCOOH production to induce CO generation. And Znδ+/ZnO presents the highest CO selectivity (FECO 70.9 % at −1.48 V vs. RHE) compared to Zn and ZnO. Furthermore, we propose a CeO2 nanotube with confinement effect and Ce3+/Ce4+ redox to stabilize Znδ+ species. The hollow core–shell structure of the Znδ+/ZnO/CeO2 catalyst enables to extremely expose electrochemically active area while maintaining the Znδ+ sites with long‐time stability. Certainly, the target catalyst affords a FECO of 76.9 % at −1.08 V vs. RHE and no significant decay of CO selectivity in excess of 18 h.

Multilevel-Regulated Metal-Organic Framework Platform Integrating Pore Space Partition and Open-Metal Sites for Enhanced CO2 Photoreduction to CO with Nearly 100% Selectivity.

Rational design and regulation of atomically precise photocatalysts are essential for constructing efficient photocatalytic systems tunable at both the atomic and molecular levels. Herein, we propose a platform-based strategy capable of integrating both pore space partition (PSP) and open-metal sites (OMSs) as foundational features for constructing high-performance photocatalysts. We demonstrate the first structural prototype obtained from this strategy: pore-partitioned NiTCPE-pstp (TCPE = 1,1,2,2-tetra(4-carboxylphenyl)ethylene, pstp = partitioned stp topology). Nonpartitioned NiTCPE-stp is constructed from six-connected [Ni3(μ3-OH)(COO)6] trimer and TCPE linker to form 1D hexagonal channels with six coplanar OMSs directed at channel centers. After introducing triangular pore-partitioning ligands, half of the OMSs were retained, while the other half were used for PSP, leading to unprecedented microenvironment regulation of the pore structure. The resulting material integrates multiple advanced properties, including robustness, wider absorption range, enhanced electronic conductivity, and high CO2 adsorption, all of which are highly desirable for photocatalytic applications. Remarkably, NiTCPE-pstp exhibits excellent CO2 photoreduction activity with a high CO generation rate of 3353.6 μmol g-1 h-1 and nearly 100% selectivity. Theoretical and experimental studies show that the introduction of partitioning ligands not only optimizes the electronic structure to promote the separation and transfer of photogenerated carriers but also reduces the energy barrier for the formation of *COOH intermediates while promoting CO2 activation and CO desorption. This work is believed to be the first example to integrate PSP strategies and OMSs within metal-organic framework (MOF) photocatalysts, which provides new insight as well as new structural prototype for the design and performance optimization of MOF-based photocatalysts.

Fe acting as functionalized auxiliary agents in nitrogen-doped carbon supported Ni-based catalysts for electrocatalytic CO2 Reduction: Effect of valence state

Converting CO2 into useful chemicals is an effective measure to address the energy crisis and the greenhouse effect. CO2RR has become a research hotspot due to its mild conditions. Ni-N-C catalysts are known as promising electrocatalysts, while achieving atomic level dispersion of Ni on the surface of the carrier is still facing challenges. In this work, various N-doped carbon supported Ni-based catalysts were synthesized by selecting Fe2+/Fe3+ as functionalized auxiliary agents in precursors. Different coordination situations of Fe(III)/Ni@NC and Fe(II)/Ni@NC are formed which derived from the valence state of Fe. During the synthesis process of Fe(III)/Ni@NC, Ni2+ replaced Fe3+ through competitive complexation, thereby achieving atomic level dispersion of Ni atoms on the catalyst surface. XAS confirms that Fe(III)/Ni@NC is a Ni-single-atom catalyst with Ni-N4 coordination. In contrast, Fe(II)/Ni@NC contains Ni3C/Ni nanoparticles coated with carbon layer, which shows a characteristic peak approaching to 2.12 Å related to the metallic Ni-Ni bonds. In the H-type cell, the FECO of Fe(III)/Ni@NC achieves 97.8 % at −0.83 V and maintains over 95 % in a wide potential window. The in-situ Fourier transform infrared (FTIR) spectroscopy confirms that the excellent product CO selectivity in CO2RR is due to the accumulation of *COOH intermediates at the active sites. Significantly, Fe(III)/Ni@NC shows excellent performance in the flow cell with FECO over 96 % from −40 to −140 mA cm−2. This work reveals the impact of Fe valence state of functionalized auxiliary agents on the electrocatalytic performance of materials, which provides a new approach for designing high-performance atomically dispersed electrocatalysts.

Enhanced selectivity and charge transfer over highly dispersed Cd0.2Zn0.8S/meta-kaolinite catalysts for CO2 photoreduction

In this work, a novel hybrid photocatalyst consisting of Cd0.2Zn0.8S grown on a defect-rich meta-kaolinite nanosheet (CZS/MK) composite was investigated for the photoreduction of CO2 to CO in the presence of simulated sunlight with high selectivity. CZS/MK displayed a CO yield of 21.3 µmol g−1h−1 with a remarkable selectivity of 97.4 % without any co-catalyst and sacrificial reagent. The addition of MK to the catalyst altered CZS hydrophilicity and improved CO selectivity. Moreover, kaolinite is relatively inexpensive, and the defects in MK can optimize pore size distribution and structure of Cd0.2Zn0.8S, resulting in improved dispersion and a higher quantity of exposed active sites on the composite material. Experimental investigations combined with DFT calculations illustrated that the adsorption configuration involving the introduction of kaolinite was more favorable for CO2 activation, which ultimately decreased the formation barrier of key intermediate *COOH. In situ Fourier transform-infrared analysis indicated that Cd0.2Zn0.8S/MK tended to produce vital *COOH intermediates, thereby achieving higher CO conversion efficiency. This study provides novel insights into the utilization of kaolinite-based catalysts for enhancing CO2 photoreduction.

Electron-Delocalization-Stabilized Photoelectrocatalytic Coupling of Methane by NiO-Polyoxometalate Sub-1 nm Heterostructures.

The oxidative coupling of methane to C2 oxygenates merits great scientific and technological potential yet remains a challenge due to its inferior selectivity. Subnanomaterials (SNMs) with "p-n-p-n"-type heteroconstructions feature enhanced external field coupling properties and tunable electronic structures, serving as promising catalysts for the selective partial oxidation of methane. Here we develop NiO-polyoxometalate (POM) subnanocoils with a thickness of 1.8 nm, showing excellent catalytic activity toward photoelectrochemical coupling of methane into a C2 product under mild conditions (1 bar, 25 °C) with a notable productivity (up to 4.48 mmol gcat-1 h-1) and a high selectivity (>99%). Under photoelectrochemical coupling, C-H bonds can be activated by NiO, and the resulted *COOH intermediates are stabilized by the delocalized electrons in POM clusters. The contiguous active sites of NiO and POM at the molecular level allow the in situ coupling of *COOH into oxalate. This work points out an economic way for the oxidation of methane under mild conditions and may enlighten the design of functional SNMs from fundamental standpoints.

Synergistic engineering of heteronuclear Ni-Ag dual-atom catalysts for high-efficiency CO2 electroreduction with nearly 100% CO selectivity

Single-atom catalysts (SACs) have emerged as attractive materials for the electrocatalytic carbon dioxide reduction (ECO2R). Dual-atom catalysts (DACs), an extension of SACs, exhibit more compelling functionalities due to the synergistic effects between adjacent metal atoms. However, the rational design, clear coordination mode, and in-depth understanding of heteronuclear dual-atom synergistic mechanisms remain elusive. Herein, a heteronuclear Ni-Ag dual-atom catalyst loaded on defective nitrogen-rich porous carbon, denoted as Ni-Ag/PC-N, was synthesized using cascade pyrolysis. The configuration of Ni-Ag dual-atom sites is confirmed as N3-Ni-Ag-N3. Ni-Ag/PC-N demonstrates a remarkable CO Faradaic efficiency (FECO) exceeding 90% over a broad range of applied potentials, i.e., from −0.7 to −1.3 V versus reversible hydrogen electrode (RHE). The peak FECO of 99.2% is observed at −0.8 V (vs. RHE). Tafel analysis reveals that the rate-determining step of ECO2R-to-CO is the formation of the *COOH intermediate, and Ni-Ag/PC-N exhibits optimal electrokinetics. In situ FTIR and in situ Raman spectra indicate accelerated production of *COOH intermediates during the ECO2R-to-CO process. Density functional theory (DFT) calculations demonstrate that the coordinated Ni atom lowers the energy barrier of *COOH intermediates formation over the Ni-Ag/PC-N surface, while the adjacent Ag atom mitigates the catalyst poisoning caused by the strong *CO affinity on the Ni atomic site.

Cooperative adsorption of interfacial Ga-N dual-site in GaOOH@N-doped carbon nanotubes for enhanced electrocatalytic reduction of carbon dioxide

To reduce activation energy barrier and promote the kinetics of electrocatalytic CO2 reduction reaction (eCO2RR), the performance of CO2 adsorption and activation on electrocatalysts should be optimized. Here, GaOOH is successfully coupled with N-doped carbon nanotubes (NC) via a facile self-assembly-calcination process. The obtained GaOOH@N-doped carbon nanotubes (Ga-NC) display the best CO faradaic efficiency of 96.1 % at −0.6 V (vs. reversible hydrogen electrode). Control-experiment and characterization results suggest Ga-N dual-site in interface between GaOOH and NC shows cooperative adsorption of CO2. C atom in CO2 is adsorbed on N site while O atom in CO2 is adsorbed on Ga site. This cooperative adsorption efficiently promotes the CO2 adsorption and activation performance, as well as the breaking of CO bond due to opposite attraction from Ga-N dual-site. Moreover, in-situ Fourier transform infrared spectroscopy confirms decreased reaction barrier for formation of *CO2– and *COOH intermediates. This work inspires us to construct interfacial dual-site structure with cooperative adsorption property for promoting eCO2RR activity.

Promoting photothermal catalytic CO2 reduction of Cd2In2S5/Cd0.3Zn0.7S heterojunction with encapsulated hydrogen evolution active site by accelerating charge transfer kinetics

The photothermal catalysis CO2 reduction is considered as an attractive means to solve the greenhouse effect and energy crisis. However, due to the slow charge transfer kinetics on the surface of the catalyst and sparse adsorption active site, the CO2 adsorption rate is low and the carrier life is short. So, the catalytic performance is limited. Here, a core–shell similar structure catalyst for photothermal CO2 reduction was constructed by growing of Cd0.3Zn0.7S (CZS) nanospheres on the surface of sulfur defect rich Cd2In2S5 (CIS) ultra-thin nanosheets, and which was coordinated by the interfacial chemical bond and the interfacial internal electric field. The Cd-S chemical bond became a direct channel to accelerate the transfer of electrons from the conduction band of CZS to the conduction band of CIS, leading to higher surface charge localization of CIS/CZS, and encapsulating the active site of hydrogen evolution of CZS. The core–shell similar structure was favorable for the spatial separation of photogenerated charges. The production of *HCO3– and *COOH intermediates on the CIS/CZS surface has been proved to be crucial for CO2 adsorption and CO generation by in situ Fourier transform infrared spectroscopy. The charge transfer mechanism of Type Ⅱ between CIS and CZS was proved by density functional theory calculation and in situ X-ray photoelectron spectroscopy. The CO yield of the optimized CIS/CZS heterojunction was 64.3 μmol·h−1·g−1, which was about 31.3 times that of pure CZS. This study provided a new idea for accelerating charge transfer dynamics and inhibiting competition reaction to promote the conversion of solar energy to fuel.

Cheap transition metal reinforced donor–acceptor covalent organic frameworks for CO2 photoreduction

Artificial photoreduction of CO2 is considered an attractive solution for simultaneously achieving carbon neutrality goals and solving the energy shortage crisis. In this study, a donor–acceptor (D–A) covalent organic framework (COF), COF-BT, comprising (1,1′-biphenyl)-3,3′,5,5′-tetracarbaldehyde and 4,4′-(2,1,3-benzothiadiazole-4,7-diyl)bis[benzenamine] was prepared, and cheap CoO was introduced into COF-BT via a two-step impregnation-calcination process to obtain Co-COF-BT with immobilized transition metals. Photoelectrochemical experimental and theoretical results indicate that the D–A structure of Co-COF-BT reduces the band gap, enhances visible light absorption, inhibits electron–hole recombination, and prolongs the life of photogenerated carriers. The introduction of CoO provides additional active sites, and the Co-S bond in Co-COF-BT provides an additional channel for ultrafast electron migration from the COF-BT unit to the CoO active center, which increases charge mobility and reduces the energy barrier formed by *COOH intermediates. Thus, the excellent photocatalytic CO2 reduction activity of Co-COF-BT is achieved with a CO yield of 2423 μmol g−1h−1 and selectivity > 99% under visible light. The superior photocatalytic performance is attributed to the synergistic effect of D–A moieties and CoO in Co-COF-BT. This study not only presents a novel COF-based photocatalyst with high charge transfer efficiency and high catalytic activity in CO2 reduction but also provides a potential strategy to fine-tune photoelectronic properties by adjusting the functional building blocks and additional metal active sites.

DFT Calculation of Carbon-Doped TiO2 Nanocomposites.

Titanium dioxide (TiO2) has been proven to be an excellent material for mitigating the continuous impact of elevated carbon dioxide concentrations. Carbon doping has emerged as a promising strategy to enhance the CO2 reduction performance of TiO2. In this study, we investigated the effects of carbon doping on TiO2 using density functional theory (DFT) calculations. Two carbon doping concentrations were considered (4% and 6%), denoted as TiO2-2C and TiO2-3C, respectively. The results showed that after carbon doping, the band gaps of TiO2-2C and TiO2-3C were reduced to 1.58 eV and 1.47 eV, respectively, which is lower than the band gap of pure TiO2 (2.13 eV). This indicates an effective improvement in the electronic structure of TiO2. Barrier energy calculations revealed that compared to pure TiO2 (0.65 eV), TiO2-2C (0.54 eV) and TiO2-3C (0.59 eV) exhibited lower energy barriers, facilitating the transition to *COOH intermediates. These findings provide valuable insights into the electronic structure changes induced by carbon doping in TiO2, which can contribute to the development of sustainable energy and environmental conservation measures to address global climate challenges.

Metal-organic-frameworks passivated CuBi2O4 photocathodes boost CO2 reduction kinetics

Photoelectrochemical reduction of CO2 to produce CO with metal-organic frameworks (MOFs) is recognized as a desirable technology to mitigate CO2 emission and generate sustainable energy. To achieve highly efficient electrocatalyst, it is essential to design a new material interface and uncover new reaction mechanisms or kinetics. Herein, we developed two metal-organic Cu-MOF and Bi-MOF layers using benzene tricarboxylic acid (H3BTC) ligands on CuBi2O4 photocathodes. Both MOF layers drastically improved the photoelectrochemical stability by suppressing the photo-corrosion through conformal surface passivation. The Cu-MOF modified CuBi2O4 showed more significant charge separation and transfer efficiencies than the Bi-MOF modified control. Based on the transient photocurrent curves under the applied potential of 0.6 V vs. RHE, the rate-law analysis showed the CO2 photoreduction took place through a first-order reaction. Further, the photoelectrochemical impedance spectra (PEIS) revealed this reaction order, representing an “operando” analysis. Moreover, the reaction rate constant on Cu-MOF modified sample was higher than that on Bi-MOF modified one and bare CuBi2O4. Combined with the density functional theory calculation, the surface absorption of CO2 and CO molecules and the higher energy barrier for ∗COOH intermediates could significantly determine the first order reaction.

Bi-reforming of methane in a carbon deposit-free plasmatron with high operational adaptability

An atmospheric plasmatron reactor with two-stage inlets was developed for bi-reforming of methane (CO2/CH4/H2O) to produce syngas (H2 + CO) and value-added liquid products. The influence of CH4 inlet position, gas flow rate and reactant composition were investigated. The results showed that the two-stage-inlet design allows for a wide range of operational conditions in terms of the CO2/CH4/H2O ratio (2–7:0–6:0–3) and total flow rate (4.5-11 L/min). A CO2 and CH4 conversion of 24% and 12.9%, respectively, was obtained at flow rates of up to 7-8 L/min, with no observable carbon deposit formed. A closer injection of CH4 to the core plasma area was more beneficial for both reactant conversion and syngas selectivity. Interestingly, value-added oxygenated products (e.g., methanol, ethanol, acetic acid) were produced simultaneously, offering a promising power-to-liquid (PtL) route. In particular, the direct synthesis of acetic acid from CH4 and CO2 was achieved, which is infeasible in thermocatalytic processes. A small addition of H2O (14.3%) favorably enhanced the formation of acetic acid by up to 160%, likely due to the improved generation of CH3 and COOH intermediates. Overall, this work offers a promising route for syngas and oxygenated products generation in a scalable plasmatron reactor with high operational adaptability.