CO2 Reduction Performance Research Articles

Harnessing the electrocatalytic potential of in-situ exsolution of Ni nanoparticles on lanthanum and calcium co-doped strontium titanate for CO2 reduction in solid oxide electrolysis cells

The exsolution phenomenon of metal nanoparticles from a perovskite oxide involves the creation of oxygen vacancies, contributing to improved catalytic activity for CO2 reduction. In this context, a B-site Ni-doped and A-site La, Ca co-doped strontium titanate, denoted as La0.20Sr0.25Ca0.45Ni0.05Ti0.95O3-δ (Ni-LSCT), is synthesized with the aim of serving as a highly efficient cathode in conjunction with LSM as the anode and YSZ as the electrolyte for CO2 reduction via solid oxide electrolysis process. The incorporation of 5 mol% Ni doping at the B-site of the perovskite is successfully achieved, leading to the subsequent release of highly dispersed nanoparticles upon exposure to a reducing environment. YSZ-electrolyte-supported SOECs featuring the Ni-LSCT cathode demonstrate a notable current density of 0.93 A/cm2 at an applied voltage of 2.5 V at 800 °C in pure CO2. Moreover, at the same temperature, the reduction current density measures 1.21 A/cm2 when the Ni-LSCT serves as the cathode in a 70/30 molar ratio (CO2/H2) environment and 1.73 A/cm2 with a 50/50 molar ratio of the feed gas, both at an applied voltage of 2.5 V. This suggests an enhanced CO2 reduction performance in a reducing atmosphere. The introduction of Ni doping into LSCT enhances the electrochemical activity of the cathode by augmenting oxygen vacancies, while the presence of Ni nanoparticles on the cathode surface intensifies the active sites. Collectively, this innovative electrocatalyst configuration presents promising prospects for CO2 electrolysis within the SOEC framework.

Insights into the effect of Ni doping on In2S3 for enhanced activity and selectivity of photocatalytic CO2 reduction

The limited photocatalytic CO2 reduction performance mainly lies in the low utilization of photogenerated electrons during the reaction. In this work, we developed the defect level within the Ni-doped In2S3 nanotube photocatalysts via a simple solvothermal method to increase the available amount of photogenerated electrons for enhanced photocatalytic CO2 reduction performance than the pristine In2S3. The introduction of Ni element into the lattice of In2S3 could significantly improve the photocatalytic activity and selectivity without destruction of the nanotube structure of In2S3. The yield of CO reaches 243.2 μmol/g/h under visible light, which is the highest reported value among In2S3 photocatalysts, and is 8.2 times more than the pure In2S3. Moreover, by modulating the doping amount of Ni element, the selectivity of CO varied from 27.7% to 51.0%. Further characterizations suggest that the doping of Ni element altered the electronic bandgap arrangement of In2S3, where the position of the conduction band is conducive to the activation of CO2 molecules. Moreover, the defect level resulting from Ni-doping not only facilitates the separation of photoexcited electron-hole pairs but also suppresses the recombination of electrons and holes. This study provides an available and reliable strategy for enhancing the photocatalytic CO2 reduction performance of related sulfide photocatalytic materials in future studies.

A linear correlation of p-band center with the performance of electrochemical CO2 reduction revealed by Sn single-atom catalysts

The correlation between p-orbital energy level and catalytic activity of electrochemical CO2 reduction reaction (ECRR) is rarely reported, but significantly desired for further design of highly effective main group single-atom catalysts (SACs). Herein, a series of Sn-SACs (Sn-N3S1, Sn-N3P1, Sn-N3B1, and Sn-N4) were developed as a model system to explore structure-activity relationships of main group SACs for ECRR. Coordination environment regulation could upshift the p-band center of Sn, facilitating the adsorption of intermediates and improving the catalytic activity. Sn-N3S1 with the most positive p-band center shows a 100 % Faradaic efficiency of CO (FECO), superior over that of Sn-N4 and other reported SACs. Notably, the catalytic performance of Sn-SACs shows a linear relationship with p-band center of Sn, indicating a high applicability of p-band center as a descriptor for catalytic performance. This work provides a new way to boost ECRR by lowering the p-orbital energy level of main group metal.

2D/1D nested hollow porous ZnIn2S4/g-C3N4 heterojunction based on morphology modulation for photocatalytic CO2 reduction

The two-dimensional (2D) composite one-dimensional (1D) heterojunction structure is one of the main strategies for constructing composite photocatalysts for photocatalytic reduction of carbon dioxide (CO2). However, morphology modulation for 2D/1D heterojunction is an important way to enhance performance. In this study, a unique 2D/1D ZnIn2S4/g-C3N4 nested hollow porous heterojunction structure was constructed by an in-situ growth method with spatial confinement effect. The synergy between 1D g-C3N4 and 2D ZnIn2S4, achieved through advanced morphology modulation at an optimal ratio of 3:1, results in the formation of the CZ-3 photocatalyst. This unique configuration enables a simultaneous high yield of carbon monoxide (CO) and methane (CH4), achieving 79.96 μmol/g and 17.33 μmol/g respectively, under visible light irradiation without the need for sacrificial agents. The core of this enhanced photocatalytic performance is attributed to the employment of a type-II heterojunction mechanism, which optimizes the transfer of photogenerated carriers. Ultraviolet-visible diffuse reflection spectrum, photoluminescence spectrum and photoelectrochemical analysis reveal the effect of morphology on photocatalytic performance in terms of visible light absorption, photogenerated carrier pairs separation and electronic band structure of heterojunction. By combining the advantages of 2D/1D structural benefits with the efficient charge dynamics of a type-II heterojunction, this work provides new ideas for improving the morphology of composite heterojunction photocatalysts with 2D/1D structure to enhance the photocatalytic CO2 reduction performance.

Photoelectrochemically converting CO2 over Z-scheme heterojunction CoPc/K7HNb6O19 with high Faraday efficiency

Photoelectrochemically converting CO2 into the high value-added chemicals and fuels is a hopeful sustainable energy conversion and storage road to alleviate the energy crisis and global warming. In this study, CoN-x Z-scheme heterojunctions were prepared by coupling CoPc with K7HNb6O19 rich in oxygen vacancy with a low-temperature calcination, and used for photoelectrocatalytic (PEC) reduction of CO2 to CO. The prepared heterojunctions demonstrate Faraday efficiency of >90 % and TOF values over a wide voltage range (−0.65 ∼ −1 V vs. RHE). The superior PEC CO2 reduction performance is mainly attributed to the designed Z-scheme heterojunction, which endows a built-in electric field to the interface of the two semiconductors, benefiting the separation of electrons and holes greatly. Additionally, the oxygen vacancy from K7HNb6O19 provides an alternative pathway for CO2 adsorption and activation, and simultaneously the incorporated K7HNb6O19 inhibits the aggregation of cobalt phthalocyanine molecules, which is beneficial for the stability of PEC catalysts. Density-functional-theory (DFT) calculation also elucidates a favorable CO2 activation energy over CoPc coupling oxygen-vacancy-rich K7HNb6O19 heterojunctions. This work may provide a viable pathway for the rational designing of efficient PEC systems to reduce CO2 to valuable fuels.

Advances in Defect Engineering of Metal Oxides for Photocatalytic CO2 Reduction.

Photocatalytic CO2 reduction technology, capable of converting low-density solar energy into high-density chemical energy, stands as a promising approach to alleviate the energy crisis and achieve carbon neutrality. Semiconductor metal oxides, characterized by their abundant reserves, good stability, and easily tunable structures, have found extensive applications in the field of photocatalysis. However, the wide bandgap inherent in metal oxides contributes to their poor efficiency in photocatalytic CO2 reduction. Defect engineering presents an effective strategy to address these challenges. This paper reviews the research progress in defect engineering to enhance the photocatalytic CO2 reduction performance of metal oxides, summarizing defect classifications, preparation methods, and characterization techniques. The focus is on defect engineering, represented by vacancies and doping, for improving the performance of metal oxide photocatalysts. This includes advancements in expanding the photoresponse range, enhancing photogenerated charge separation, and promoting CO2 molecule activation. Finally, the paper provides a summary of the current issues and challenges faced by defect engineering, along with a prospective outlook on the future development of photocatalytic CO2 reduction technology.

Facile synthesis of MOF–808/RGO-based 3D macroscopic aerogel for enhanced photoreduction CO2

Three-dimensional (3D) macroscopic aerogels have emerged as a critical component in the realm of photocatalysis. Maximizing the integration of materials can result in enhanced efficiency and selectivity in photocatalytic processes. In this investigation, we fabricated MOF-808/reduced graphene oxide (RGO) 3D macroscopic aerogel composite materials employing the techniques of hydrothermal synthesis and freeze-drying. The results revealed that the macroscopic aerogel material exhibited the highest performance in CO2 reduction to CO, particularly when the concentration of RGO was maintained at 5 mg mL−1. In addition, we synthesized powder materials of MR-5 composite photocatalysts and conducted a comparative analysis in terms of photocatalytic CO2 reduction performance and electron transfer efficiency. The results showthat the macroscopic aerogel material boasts a high specific surface area, an abundant internal pore structure, and increased active sites. These attributes collectively enhance light energy utilization, and electron transfer rates, thereby, improving photothermal and photoelectric conversion efficiencies. Furthermore, we conducted in-situ FT-IR measurements and found that the M/R-5 aerogel exhibited the best CO2 adsorption capacity under a CO2 flow rate of 10 mL min−1. The density functional theory results demonstrate the correlation between the formation pathway of the product and the charge transfer pathway. This study provides useful ideas for realizing photocatalytic CO2 reduction of macroscopic aerogel materials in gas–solid reaction mode.

Hydrothermal synthesis of Ce-doped SnS2 2D nanoplates with enhanced photocatalytic CO2 reduction performance

CO2 emissions caused by human activities seriously influence the climate of earth and hinder the sustainable development of humans and nature. Photocatalytic CO2 reduction is an effective method to convert CO2 into other chemicals and reduce CO2 emissions. Here, Ce doped SnS2 photocatalyst has been obtained by using a hydrothermal method. The phase and structure of obtained samples have been characterized and the photocatalytic CO2 reduction performance has been evaluated. The results show that Ce dopants can improve visible light absorption, increase the specific surface area, especially increase the adsorption of CO2. The influence of Ce doping concentration was investigated to optimize the photocatalytic performance. Compared to the pristine SnS2 photocatalyst, the Ce–SnS2 reached 46.9 μmol g−1 h−1 in the CO2 photo-reduced test, which is 3.21 times that of pristine SnS2 photocatalyst. The enhanced photocatalytic performance can be attributed to Ce dopant which increases the specific surface and CO2 absorption quantity, and reduces the recombination of photogenerated electrons and holes.

Insights into bimetallic single-atom-doped g-C3N4 photo-catalysts for CO2 conversion to HCOOH: A DFT study

Developing low-cost, high-efficiency non-noble metallic photocatalytic materials is crucial for CO2 reduction. This paper investigates the substitution of noble metals dopant to a bimetallic non-noble Fe/Co dopant for g-C3N4 to enhance the photocatalytic CO2 reduction performance via density functional theory (DFT) calculations. This study examines the structure, electronic properties, CO2 adsorption configurations, and the transition states and Gibbs free energy of CO2 reduction to HCOOH on noble metal Pt/g-C3N4 doped, single-atom Fe/g-C3N4 doped, and bimetallic Fe/Co doped g-C3N4 catalysts, revealing the mechanisms of catalyst-mediated CO2 reduction. The results demonstrate that the introduction of Fe/Co bimetallic atoms leads to more efficient charge transfer, attributed to the synergistic and electronic effects of the bimetallic coupling, with a charge of 1.264, which is 2.2 and 1.2 times greater than that of Pt and Fe doped g-C3N4, respectively. Furthermore, the stronger adsorption energy of CO2 molecules on Fe/Co/g-C3N4 compared to pure g-C3N4, Pt/g-C3N4, and Fe/g-C3N4 indicates that adsorption on Fe/Co/g-C3N4 is more conducive to CO2 activation. The CO2 reduction reaction (CO2RR) calculations reveal that Fe/Co/g-C3N4 exhibits a lower reaction barrier of 0.789 eV compared to noble metal-doped Pt and single-atom Fe, due to the reduction of the reaction mechanism's energy barrier by the Fe/Co bimetallic doped g-C3N4, which facilitates a more effective reduction of CO2 to HCOOH. As a result, Fe/Co/g-C3N4 emerges as an effective alternative to noble metal-based photocatalysts. This study provides theoretical guidance for the preparation of efficient non-noble metal photocatalysts.

CO2 Reduction Performance with Double-Layered Cu/TiO2 and P4O10/TiO2 as Photocatalysts under Different Light Illumination Conditions

CO2 Reduction Performance with Double-Layered Cu/TiO2 and P4O10/TiO2 as Photocatalysts under Different Light Illumination Conditions

Unveiling the kinetics of CO2 reduction in aprotic electrolyte: The critical role of adsorption

Aprotic organic electrolytes for electrocatalytic CO2 reduction (CO2R) offer a promising yet little-explored alternative to avoid the selectivity issues of alkaline media. We present a model-assisted study of the local reaction environment at a Cu cathode in aprotic organic electrolytes to determine the kinetics of the CO2R and the kinetic limitations and reveal their dependence on reaction conditions. The adsorption of CO2 is identified as the rate-determining step, as opposed to the often-assumed electron transfer during radical anion formation. Unlike alkaline media, there is no transport limitation in aprotic media. Furthermore, our model predicts two strategies to overcome the adsorption limitation: (i) by increasing surface roughness and (ii) by elevating pressure. The findings highlight the critical role of CO2 adsorption on CO2R performance and enable knowledge-driven optimization of reaction conditions and electrocatalysts.

Dinuclear Cu(I) molecular electrocatalyst for CO2-to-C3 product conversion

Molecular metal complex catalysts are highly tunable in terms of their CO2 reduction performance by means of their flexible molecular design. However, metal complex catalysts have challenges in their structural stability and it has not been possible to synthesize high-value-added C3 products due to their inability to perform C–C coupling. Here we show a CO2 reduction reaction catalysed by a Br-bridged dinuclear Cu(I) complex that produces C3H7OH with high robustness during the reaction. The C–C coupling reaction mechanism was analysed by experimental operando surface-enhanced Raman scattering analysis, and theoretical quantum-chemical calculations proposed the formation of a C–C coupling intermediate species with substrate incorporation between the two Cu centres. Molecular design guidelines based on this discovery offer an approach to developing next-generation catalysts that generate multicarbon CO2 reduction products.

Engineering ZIF-67 loaded nanofibrous membrane with thermal stabilization treatment for efficient photocatalytic CO2 reduction

The photocatalytic Metal-organic frameworks (MOFs) membrane addresses challenges faced by MOF powders in practical applications such as aggregation and difficult recovery, but its current application is mainly confined to wastewater treatment. Expanding the application of MOFs membranes to CO2 reduction could unleash their greater potential in energy conversion and storage field. In this study, ZIF-67 was deposited on polyacrylonitrile (PAN) nanofiber membranes (NFMs) using an in-situ growth technique, followed by thermal stabilization to produce SZIF-67/PAN NFMs for photocatalytic CO2 reduction. ZIF-67 was uniformly and densely distributed on the NFMs, with a mass loading of up to 8 wt%. The thermal stabilization process significantly enhanced the photothermal conversion capability and solvent resistance of the NFMs, enabling SZIF-67/PAN NFMs to exhibit outstanding photocatalytic activity even under mild environmental conditions, with a remarkable CO generation rate of 39,250 μmol g−1h−1. Furthermore, the performance remained at 70 % even after five consecutive tests. This study presents a novel and effective method for preparing MOF NFMs with excellent photocatalytic CO2 reduction performance, offering valuable insights for advancing the practical application of MOF materials.

Ligand-engineered Cu-based halide perovskite for highly efficient near-infrared photocatalytic CO2 reduction

A key challenge in harvesting solar energy for efficient chemical conversion is the lack of photocatalysts with wide activation wavelengths. Herein, we propose for the first time to utilize halide perovskite to absorb the full spectrum (200–2500 nm), including ultraviolet (UV), visible (Vis), and near-infrared (NIR) light, to directly power photocatalytic CO2 reduction. This full-spectrum light-responsive occurs on metal halide perovskite Cs2CuCl4 microcrystals (MCs), and the ligand soybean lecithin is applied to optimize the active phase of Cs2CuCl4 photocatalyst, such as morphology, particle size, crystal face and electronic structure. As revealed by optical absorption analysis, the Cs2CuCl4 and ligand soybean lecithin modified Cs2CuCl4 (SL-Cs2CuCl4) MCs exhibit significant optical absorption in the UV, Vis light and NIR light regions. The photocatalytic CO2 reduction performance was assessed under simulated sunlight (200–2500 nm), and the SL-Cs2CuCl4 MCs achieved a CO fuel yield of 254.46 µmol g−1, which increased the yield by 5 times relative to the initial sample. Based on in-situ Fourier transform infrared, electron spin resonance and X-ray photoelectron spectroscopy, the active substances and reaction intermediates at the active site of SL-Cs2CuCl4 MCs were dynamically monitored, and the photocatalytic mechanism was revealed together with density functional theory (DFT) calculations. The DFT calculation shows that the photocatalytic reduction of CO2 to CO by Cs2CuCl4 is proposed to involve the concerted action of both Cs and Cu sites.

Activating the Ni‐Contenting Carbon Nanotube by Covalent Triazine Frameworks to Form Atomically Dispersed Ni Sites with Curvature Effect for Electrocatalytic CO2 Reduction

N‐coordinated Ni sites (NiNx) are effective catalysts for the electrochemical reduction of CO2 to CO. In most researches, modulating the coordination environment of Ni atoms is focused on to improve electrochemical CO2 reduction (ECR) performance. However, the influence of the carbon substrate's structure on the intrinsic activity of NiNx is seldom investigated. The highly curved surface of carbon nanotubes (CNT) may provide a unique curvature effect on NiNx. It is found that the Ni residues in CNT can be atomized to form NiNx sites on the surface of CNT (Ni‐N/CNT@covalent triazine framework [CTF]) through high‐temperature pyrolysis, using a soluble CTF nanosheet as N precursor. The π‐conjugated and ultrathin 2D structure of CTF enables closer interfacial contact between CTF and CNT, which avoids the formation of a thick carbon layer to maximize the curvature effect. Theoretical data reveal that the NiN3 configuration may act as a highly active ECR site, and the curvature effect from CNT can further tune the electronic structure of NiN3, thus improving the ECR kinetics. The Ni‐N/CNT@CTF‐based flow‐cell electrolyzer exhibits a jCO of 201 mA cm−2 at −0.9 V with a high FECO of 98%.

NH2-UiO-66 modification BiOBr enhancement photoreduction CO2 to CO

As a typical semiconductor catalyst, BiOBr has an advisable bandgap, superior light absorption properties, and a unique laminated structure. However, the slow electron-hole separation rate results in poor CO2 reduction performance. To enhance the photocatalytic efficiency of BiOBr, this study constructs BiOBr heterojunctions with Lewis basic groups by loading NH2-UiO-66 on BiOBr. The BiOBr/NH2-UiO-66 heterojunction have been built and possess stronger light response, larger specific surface area and electron-hole separation efficiency compared to pure BiOBr and NH2-UiO-66. The optimal BiOBr/NH2-UiO-66 displays that the CO yield is 9.19 μmol g-1h−1, which is 4 times higher than pure BiOBr.

BiOCl/BiOBr composites for efficient photocatalytic carbon dioxide reduction

BiOBr (BOB) photocatalysts have low photocatalytic CO2 reduction performance due to their low electron-hole pair separation efficiency. To improve this problem, BiOCl (BOCl) is used as a co-catalyst. BOCl is loaded into BOB to form BiOCl/BiOBr (BOCl/BOB) type Ⅰ heterojunction, which enhances the photocatalytic CO2 reduction performance of BOB by promoting the separation of photogenerated electrons and holes. The results of TPR and PL experiments show that the 20% BOCl/BOB composites have the highest photogenerated carrier separation rate, and the results of CO2 reduction experiments show that 20% BOCl/BOB composites have the best photocatalytic CO2 reduction performance of 7.353 μmolg−1h−1, which is 3.22 and 1.99 times higher than pure BOB and BOCl, respectively. This work provides an effective reference for the development of modified photocatalysts.

Cr dopants and S vacancies in ZnS to trigger efficient photocatalytic H2 evolution and CO2 reduction

Driven by endless solar energy, photocatalytic H2 evolution from water splitting and CO2 conversion to hydrocarbon fuels over semiconductor photocatalysts are of great potential to simultaneously settle the greenhouse effect and energy shortage. Herein, Cr-doped zinc sulfide (ZnS) with accompanying sulphur vacancies (Vs) photocatalytic materials is developed by a facile hydrothermal method. The Cr dopants centralize photoinduced holes and Vs trap electrons, forming a synergistic effect for accelerating charge separation and transfer. The reaction energy barrier for both H2 evolution and CO2 reduction has been optimized. Therefore, in the absence of a cocatalyst, the optimal catalyst (Zn0.94Cr0.06S) achieves an outstanding H2 evolution activity of 20.3 mmol g−1 h−1, which is approximately 2.9 times higher than 6.9 mmol g−1 h−1 for pristine ZnS. In addition, in the gas-solid reaction system without co-catalysts or sacrificial agents, the Zn0.94Cr0.06S exhibits a considerable CO evolution rate of 19.56 μmol g−1 h−1, about 10.1 times higher than ZnS (1.94 μmol g−1 h−1). Both the performances for H2 evolution and CO2 reduction of Zn0.94Cr0.06S outperform most of the previously reported photocatalysts. Particularly, the Zn0.94Cr0.06S possesses superior stability, the photoactivity of which exhibits no noticeable deactivation after six cycles’ reactions. This work may shed light on the rational design and fabrication of highly efficient materials via combining individual element doping and defect engineering.

Bi2O2S/CAU-17 bifunctional heterojunction for boosting CO2 photoreduction performance origin from the simultaneous photoxidation of tetracycline

To address the issues of energy scarcity and environmental pollution, a photocatalytic coupling system is employed to simultaneously harness electrons and holes in a single photocatalytic system. The current study presents a novel approach to construct a dual reaction pathway system for tetracycline hydrochloride (TC) oxidation and CO2 reduction. Herein, Bi2O2S/CAU-17 composite was designed and fabricated through a facile solvothermal method. The hybrid photocatalyst exhibited an excellent performance for simultaneous TC degradation and CO2 reduction. The CO-production rate can be reached 22.0 μmol g-1h−1 through the optimized 20% Bi2O2S/CAU-17 sample. Notably, the source of CO2 in the reaction system is solely derived from the photoxidation of TC. The theoretical calculations and experimental findings have shown that the existed Bi2O2S can enrich electron and separation of photo-generated electrons from CAU-17, thus, the holes in Bi2O2S and CAU-17 can be involved in the photodegradation of TC. Afterwards, the CO2 generated by TC oxidation moves to Bi2O2S via diffusion of molecules and could be efficiently reduced by electrons to produce CO. The development of this novel bifunctional Bi2O2S/CAU-17 hybrid photocatalytic system could provide valuable insights for the advancement of photocatalytic coupling reaction systems.

Construction of carbonized polymer dots/potassium doped carbon nitride nanosheets Van der Waals heterojunction by ball milling method for facilitating photocatalytic CO2 reduction performance in pure water

When the advancement of conventional heterojunctions is restricted by lattice matching of materials, Van der Waals heterojunctions formed by interlayer Van der Waals force present enormous development prospects with the revolution of graphene and graphene-like materials. Ascribed to similar graphene-like structures, carbonized polymer dots (CPDs) and potassium-doped carbon nitride nanosheets (KCNNS) were stacked by the ball milling method to form a novel Van der Waals heterojunction. Experimental analysis and density functional theory (DFT) calculations demonstrate that the constructed CPDs/KCNNS heterojunctions can effectively suppress sluggish reaction dynamics. CPDs/KCNNS-2 composites demonstrate enhanced CO2 photoreduction performance (78.98 μmol g−1∙h−1) with 100% CO selectivity in pure water, which is 13.71 times higher than that of KCNNS. In-situ FT-IR spectra were employed to identify the intermediates formed in the CO evolution process of CPDs/KCNNS composites. The manuscript provides a scientific reference for the stacking of Van der Waals heterojunction based on C3N4 in the artificial photosynthesis field.