CO Generation Rate Research Articles

Anion vacancy correlated photocatalytic CO2 to CO conversion over quantum-confined CdS nanorods under visible light

In terms of electronic structure change, surface anion vacancies in II–VI semiconductors could promote CO generation rates, which have been confirmed as active sites for photocatalytic CO2 reduction.

CdO decorated CdS nanorod for enhanced photocatalytic reduction of CO2 to CO.

Solar-driven CO2 reduction into fuels and sustainable energy has attracted increasing attention around the world. However, the photoreduction efficiency remains low due to the low efficiency of separation of electron-hole pairs and high thermal stability of CO2. In this work, we prepared a CdO decorated CdS nanorod for visible light driven CO2 reduction. The introduction of CdO facilitates the photoinduced charge carrier separation and transfer and acts as an active site for adsorption and activation of CO2 molecules. Compared with pristine CdS, CdO/CdS exhibits a nearly 5-fold higher CO generation rate (1.26 mmol g-1 h-1). In situ FT-IR experiments indicated that CO2 reduction on CdO/CdS may follow a COOH* pathway. This study reports the pivotal effect of CdO on photogenerated carrier transfer in photocatalysis and on CO2 adsorption, which provides a facile way to enhance photocatalytic efficiency.

Partially Nitrided Ni Nanoclusters Achieve Energy-Efficient Electrocatalytic CO2 Reduction to CO at Ultralow Overpotential.

Electrocatalytic CO2 reduction reaction (CO2 RR) offers a promising strategy to lower CO2 emission while producing value-added chemicals. A great challenge facing CO2 RR is how to improve energy efficiency by reducing overpotentials. Herein, partially nitrided Ni nanoclusters (NiNx ) immobilized on N-doped carbon nanotubes (NCNT) for CO2 RR are reported, which achieves the lowest onset overpotential of 16mV for CO2 -to-CO and the highest cathode energy efficiency of 86.9% with CO Faraday efficiency >99.0% to date. Interestingly, NiNx /NCNT affords a CO generation rate of 43.0molg-1 h-1 at a low potential of -0.572V (vs RHE). DFT calculations reveal that the NiNx nanoclusters favor *COOH formation with lower Gibbs free energy than isolated Ni single-atom, hence lowering CO2 RR overpotential. As NiNx /NCNT is applied to a membrane electrode assembly system coupled with oxygen evolution reaction, a cell voltage of only 2.13V is required to reach 100mAcm-2 , with total energy efficiency of 62.2%.

Experimental study and thermodynamic analysis of coal spontaneous combustion characteristics

Spontaneous coal combustion is one of the most common disasters in coal mine production. In order to explore the mechanism of coal spontaneous combustion more deeply, coal samples from the Yangdong wellfield of Jizhong Energy were selected for oxidative heat energy analysis experiments. A temperature-programmed experiment was selected to study the changes in characteristic parameters during the low-temperature oxidation of coal under different air supply conditions. TG-DSC experiments were conducted to study the characteristic temperature changes and thermodynamic characteristics of coal combustion processes at different heating rates. The study results show that the coal is most easily oxidised in the low-temperature oxidation stage when the air supply is 120 ml/min. The oxygen consumption rate, CO generation rate, and maximum and minimum heat release intensity are all greater at this airflow than under other conditions. The process of spontaneous combustion of coal has six characteristic temperature points and is divided into five stages. The characteristic temperature of the coal sample increased with the increase of the heating rate, and the TG/DTG curve showed a hysteresis phenomenon. DSC temperature curve shifts toward the high temperature with the increase of the heating rate, and the exothermic region is expanded. Isokinetic analysis (F-W-O and V-W) and Coats-Redfern model for calculating thermodynamic parameters. The activation energy of the samples decreased with the increase of the heating rate in the range of 2∼20°C·min−1 and showed a decreasing trend with the increase of the conversion rate.

Vacancy Pair-Induced Charge Rebalancing with Surface and Interfacial Dual Polarization for CO2 Photoreduction

Poor charge kinetics greatly reduce the efficiency of photocatalytic CO2 reduction. Herein, a synchronous surface and interfacial dual polarization strategy was developed to promote charge separation. Bi–O vacancy pairs in Bi24O31Br10 atomic layers can trigger strong coupling between black phosphorus (BP) and Bi24O31Br10, forming a restructured closely contacted BP–Bi24O31Br10 configuration with a charge-redistributed interface via electronegativity-induced charge rebalancing. The Bi–O vacancy pairs on the surface of Bi24O31Br10 and restructured BP/Bi24O31Br10 interface enable synchronous surface and interfacial dual polarization, creating an electronic bridge from the interior of Bi24O31Br10 to the BP surface, as proven by ultrafast transient absorption spectroscopy. This configuration favors a low CO2 activation energy barrier, effectively stabilizes COOH* intermediates, and decreases the rate-determining step energy barrier. Benefiting from these features, the stable CO generation rate of optimized BP–Bi24O31Br10 reaches up to 39.8 μmol g–1 h–1 via CO2 photoreduction in water, which is 2.4 and 46.8 times higher than those of defective Bi24O31Br10 atomic layers and defect-poor Bi24O31Br10, respectively. This study provides insights into the synchronous design of surface defects and restructured interfaces for dual polarization.

Synergistic Effect in Plasmonic CuAu Alloys as Co-Catalyst on SnIn4S8 for Boosted Solar-Driven CO2 Reduction

The photoreduction of CO2 to chemical fuels represents a promising technology to mitigate the current energy dilemma and global warming problems. Unfortunately, the original photocatalysts suffer from many side reactions and a poor CO2 conversion efficiency. The rational combination of active co-catalyst with pristine photocatalysts for promoting the adsorption and activation of CO2 is of vital importance to tackle this grand challenge. Herein, we rationally designed a SnIn4S8 nanosheet photocatalyst simultaneously equipped with CuAu alloys. The experimental results proved that the CuAu alloy can trap the electrons and enhance the separation and transport efficiency of the photogenerated carrier in the photocatalyst, alleviating the kinetical difficulty of the charge transfer process because of the preferable localized surface plasmon resonance (LSPR). Furthermore, the CuAu alloy works as the synergistic site to increase the CO2 adsorption and activation capacity. The optimized CuAu-SnIn4S8 photocatalyst exhibited a superior performance with CO generation rates of 27.87 μmol g−1 h−1 and CH4 of 7.21 μmol g−1 h−1, which are about 7.6 and 2.5 folds compared with SnIn4S8. This work highlights the critical role of alloy cocatalysts in boosting a CO2 activation and an efficient CO2 reduction, thus contributing to the development of more outstanding photocatalytic systems.

Efficient photocatalytic reduction of CO2 by improving adsorption activation and carrier utilization rate through N-vacancy g-C3N4 hollow microtubule

The g-C3N4 is considered to be a promising non-metallic semiconductor photocatalyst for converting CO2 into value-added products. However, g-C3N4 undergoes recombination of photogenerated electrons and holes and its low CO2 adsorption capacity. Here, g-C3N4 hollow microtube (TCN) structure with tunable N-vacancy concentrations (TCN-1) was controllably fabricated by hydrothermal self-assembly followed by H2 heat treatment. The resultant N-vacancy with one-dimensional structure g-C3N4 exhibits excellent activity for photocatalytic CO2 reduction, giving the CO generation rate of 7.06 μmol/g/h (TCN-1) under visible-light illumination without any co-catalyst or a sacrificial agent, which is 2.2- and 8.8- times that of TCN (3.12 μmol/g/h) and pristine g-C3N4 (0.75 μmol/g/h). It is well evidenced with experiments and DFT calculations that N-vacancy mainly originates from the selective cleavage of C=N–C sites on the surface of g-C3N4. The N-vacancy can act as electron trap, extending the lifetime of charge carriers. Moreover, the changes in the electron distribution around the vacancies thereby provide the driving force for the dissociation of excitons, which in turn promotes the activation of CO2 adsorption. The bifunctional of g-C3N4 with structural optimization and defect design is a very promising candidate for enhancing the adsorption-activation of reactants and the carrier utilization of photocatalysts in the photocatalytic process.

Multichannel electron transmission and multiple light scattering in CoCo PBA/CoSn(OH)6/Pt photocatalyst for effective conversion of simulated flue gas

Converting industrial waste gas into high-value chemicals is crucial to sustainable economic development. Herein, through a coordination strategy of facet-selective etching and in-situ growth, the CoCo Prussian blue analogue (PBA)/CoSn(OH)6/Pt heterojunction was designed and prepared with multiple interfaces and dual interconnection networks, which is suitable for photocatalytic conversion of simulated flue gas. This unique structure is conducive to multi-channel electron transmission and multiple light scattering, promoting the separation and migration of photogenerated carriers. This photocatalyst can synergistically regulate charge potential and kinetics, and enhance CO2 activation. Therefore, the CO generation rate (11.7 µmol·g−1·h−1) and selectivity (91.8 %) of the CoCo PBA/CoSn(OH)6/Pt heterojunction were significantly improved without using additional photosensitizer or sacrificial agent. The mechanism and reaction pathway of photocatalytic CO2 reduction were further studied by in-situ technology and density functional theory (DFT) calculation. This study offers knowledge about the preparation of high-efficiency photocatalysts for flue gas conversion and structure-modulated photocatalytic reaction.

Synergistic Inhibiting and Sealing Material for Preventing the Compound Disaster of Gas and Coal Spontaneous Combustion: Ratio Optimization and Inhibition Test

ABSTRACT The spontaneous combustion and gas explosion induced by crushed small coal pillars and the residual coal of adjacent goaf will cause a large amount of coal loss and casualties of workers. Moreover, it also seriously pollutes the environment and aggravates the greenhouse effect. To effectively block small coal pillars and fracture zones of adjacent old workings is the key to prevent gas and coal spontaneous combustion in small coal pillars. However, the commonly used blocking materials at present are easy to shrink and chap after air drying, and they have no chemical inhibitory property. Thus, these materials cannot realize the coordinated prevention of gas and coal spontaneous combustion. In this paper, a low-cost and eco-friendly Synergistic Inhibiting and Sealing Material (SISM)with strong inhibitory properties is proposed. The optimal ratio of the material was determined by experiments. The inhibitory properties of the material are analyzed by testing and comparing the generation rate of free radical and CO generation rate. The experimental results showed that the optimal molar ratio of main antioxidant and auxiliary antioxidant was 5:2, and the optimal mass ratio of synergistic antioxidant and high water material was 1:8. Secondly, SISM can prevent or delay the production of new free radicals during coal spontaneous combustion, significantly reduce the concentration of free radicals in coal and finally delay the process of coal spontaneous combustion. Thirdly, both physical and chemical inhibitory properties are taken into account when preparing SISM. Hence, it can maintain both high inhibitory properties in the whole temperature range and the inhibition effect on coal-oxygen compound reaction, which is significantly better than MgCl2 and yellow mud (YM) with only physical inhibition.

Accelerated charge transfer of g-C3N4/BiVO4 Z-scheme 2D heterojunctions by controllably introducing phosphate bridges and Ag nanocluster co-catalysts for selective CO2 photoreduction to CO

Artificial Z-scheme heterojunctions by mimicking photosynthesis have been widely investigated for photoreduction of CO2, yet the activity is hindered by the weak interfacial interactions and insufficient CO2 activation sites. Here, a cascade Z-scheme g-C3N4/BiVO4 (CN/BVO) heterojunction has been tailored by the dual modification of phosphates and Ag nanoclusters for CO2 reduction in pure water, in which phosphates are modified in the interface of CN/BVO by a facile impregnation method, while Ag nanoclusters are anchored on the surface of CN by a light induced in-situ deposition strategy under a low-temperature environment created by liquid N2. The optimal Ag-CN/PO-BVO heterojunction delivers a ca.48 μmol g−1h−1 CO generation rate with 97 % selectivity, which exhibits a 24-fold increment in CO production rate compared with that of pristine BVO. The improved photoactivity is mainly ascribed to the accelerated Z-scheme charge transfer from the built PO-bridged dimension-matched 2D interfaces and from the introduced Ag nanoclusters with preferable catalytic functions for CO2 reduction mainly by means of the time-resolved surface photovoltage responses and fluorescence spectra. Moreover, temperature-programmed desorption curves and in-situ DRIFTS results demonstrate that the introduced Ag is favorable for CO2 activation and CO desorption with COOH intermediates, responsible for the high CO selectivity.

Covalent coupling promoting charge transport of CdSeTe/UiO-66 for boosting photocatalytic CO2 reduction

Quantum dots (QDs) based heterojunction is a candidate for the photocatalytic CO2 reduction, owing to the large extinction coefficient and easy modification of band structures. However, the van der Waals interaction causes the large charge resistance and strong recombination centers between QDs and host materials, which makes the poor photocatalytic performance. Herein, a covalent bonded CdSeTe QDs and NH2-UiO-66 heterojunction (NUC-x) is constructed through an acylamino (-CONH-). The results indicate that the acylamino between NH2-UiO-66 and CdSeTe QDs can serve as the transfer channels for the photogenerated charges and stabilize the QDs. The optimized NUC-1200 achieved a CO generation rate of 228.68 µmol/g, which is 13 and 4 times higher than that of NH2-UiO-66 and CdSeTe QDs, respectively. This work provides a new avenue for efficient and stable photocatalysis of QDs.

2D/2D V2C mediated porous g-C3N4 heterojunction with the role of monolayer/multilayer MAX/MXene structures for stimulating photocatalytic CO2 reduction to fuels

2D vanadium carbide (V2C) MXene nanosheets coupled 2D porous g-C3N4 (PCN) was designed and tested for photocatalytic CO2 reduction under visible light. Controlled coupling g-C3N4 with V2C MXene resulted in higher visible light absorption and efficient charge separation. Comparatively, V2C MXene found more favorable than V2AlC MAX due to more proficient charge separation. Highest performance was achieved with optimized 15%-V2C/g-C3N4, in which CO and CH4 generation rates of 151 and 205 µmol g−1, respectively, were attained. This enhancement was significantly higher than using V2AlC/g-C3N4 and pure g-C3N4 samples due to higher conductivity and large CO2 adsorption capacity. The performance of V2C/g-C3N4 composite was further examined under a variety of conditions such as pressure, catalyst loading, and reducing agents. With increasing pressure, higher yield of CO and CH4 was attained due to increased reactant adhesion to the catalyst surface, whereas increasing catalyst loading has adverse effects. Water was the best reducing agent for CO evolution, while the methanol–water system enhanced CH4 generation. Furthermore, the stability of composite lasted for several cycles without showing any obvious deterioration. The potential outcomes are assigned to a porous structure with intimate contact, effective charge carrier separation and porous 2D g-C3N4 transporting electrons towards MXene surface. This study shows that 2D V2C MXene could be a potential carrier for constructing 2D/2D heterojunctions in photocatalytic CO2 reduction to produce useful solar fuel.

Experimental investigation and evaluation of influence of oxygen concentration on characteristic parameters of coal spontaneous combustion

Understanding the oxidation characteristics of coal spontaneous combustion and the variation of characteristic parameters is of great importance to further clarify the intrinsic mechanism of coal spontaneous combustion and to ensure safe production in coal mines. In this paper, the oxidation process of coal samples was tested at four oxygen concentrations of 21%, 15%, 10% and 5% using a programmed temperature rise experiment. Important parameters of coal spontaneous combustion, such as oxygen consumption rate, gas production rate and exothermic intensity, were calculated for the coal oxidation process. The relationship between coal temperature and oxygen concentration and the spontaneous combustion characteristics of the coal was analyzed and discussed in detail. The results show that oxygen concentration is positively correlated with the concentration of gas production. The oxygen consumption rate, CO generation rate, CO2 generation rate and exothermic intensity of the coal samples varied exponentially with temperature, due to the fact that the higher the temperature, the more intense the chemical reaction between coal and oxygen. The oxygen consumption rate and the exothermic intensity of the coal samples at different oxygen concentrations show a linear increasing relationship, which has been justified by previous investigations. A simple mathematical expression relating the oxygen consumption rate to the heat release intensity was developed and the associated proportionality factor was defined as the exothermic factor A, which was employed as an indicator for the initial determination of the intensity of the oxidation reaction of spontaneous coal combustion for different oxygen concentrations and coal types. The greater the oxygen concentration the greater the A, which can be expressed as a linear equation. For both coal samples selected for this paper, increasing the oxygen concentration increases the degree of oxidation reaction. However, Sample YQ is more sensitive to oxygen concentration than Sample CC, and the exothermic factor A at low oxygen concentrations (5-10%) is much lower than at high oxygen concentrations (15%-21%), so special attention should be paid to the prevention of coal spontaneous combustion at high oxygen concentrations by nitrogen and carbon dioxide injection during coal mining. Sample CC has a higher A at both low and high oxygen concentrations, and has a higher risk of spontaneous combustion in both oxygen environments. Comparatively, Sample CC has a higher risk of spontaneous combustion at low oxygen concentrations than Sample YQ. The research results are expected to provide some support for understanding the oxidation process of coal spontaneous combustion and preventing fire hazards in the coal mining industry.

Engineering Single-Atom Active Sites on Covalent Organic Frameworks for Boosting CO2 Photoreduction.

Solar carbon dioxide (CO2) conversion is an emerging solution to meet the challenges of sustainable energy systems and environmental/climate concerns. However, the construction of isolated active sites not only influences catalytic activity but also limits the understanding of the structure-catalyst relationship of CO2 reduction. Herein, we develop a universal synthetic protocol to fabricate different single-atom metal sites (e.g., Fe, Co, Ni, Zn, Cu, Mn, and Ru) anchored on the triazine-based covalent organic framework (SAS/Tr-COF) backbone with the bridging structure of metal-nitrogen-chlorine for high-performance catalytic CO2 reduction. Remarkably, the as-synthesized Fe SAS/Tr-COF as a representative catalyst achieved an impressive CO generation rate as high as 980.3 μmol g-1 h-1 and a selectivity of 96.4%, over approximately 26 times higher than that of the pristine Tr-COF under visible light irradiation. From X-ray absorption fine structure analysis and density functional theory calculations, the superior photocatalytic performance is attributed to the synergic effect of atomically dispersed metal sites and Tr-COF host, decreasing the reaction energy barriers for the formation of *COOH intermediates and promoting CO2 adsorption and activation as well as CO desorption. This work not only affords rational design of state-of-the-art catalysts at the molecular level but also provides in-depth insights for efficient CO2 conversion.

Two-Dimensional Porphyrin-Based Covalent Organic Framework with Enlarged Inter-layer Spacing for Tunable Photocatalytic CO2 Reduction.

Two-dimensional (2D) porphyrin-based covalent organic frameworks (COFs) are one of the most promising candidates for photocatalytic carbon dioxide reduction reaction (CO2RR), which however still suffer from the hindered mass transfer during the catalysis procedure associated with the close packing of 2D COF layers due to the strong axial π-π stacking. Herein, condensation between the porphyrinic aldehydes p-MPor-CHO (M = H2, Co, and Ni) and 3,8-diamino-6-phenyl-phenanthridine (DPP) affords new porphyrin-based 2D COF architecture MPor-DPP-COFs (M = H2, Co, and Ni). The bulky phenyl substituent at the phenanthridine periphery of the linking unit reduces the axial π-π stacking, providing an enlarged inter-layer spacing of 6.0 Å according to high-resolution transmission electron microscopy. This, in combination with the large surface area (1021 m2 g-1) revealed by nitrogen sorption measurements at 77 K for CoPor-DPP-COF possessing electroactive Co ions, endows it with excellent photocatalytic activity for CO2RR with a CO generation rate of 10 200 μmol g-1 h-1 and a CO selectivity up to 82%. This work affords new ideas for achieving efficient photocatalytic CO2RR upon fine-tuning the inter-layer spacing of 2D COFs.

Study on generation, migration and accumulation of CO in the mining goaf of shallow-buried close distance coal seam group

There is complex air leakage in the mining of shallow buried close distance coal seam group, which affects the generation and migration of CO in the goaf, and easily leads to exceeding safety limits of CO in the return corner of the working face, which threatens the safety of underground production. To examine this problem, taking Lijiahao Coal Mine as an example, this study analyses the generation law of CO gas, the distribution law of overburden fractures, the characteristics of air leakage in the goaf, the sources of CO in the return corner, and the migration and accumulation law of CO in the goaf under multi-source air leakage in the mining of shallow buried close distance coal seam group through experiment tests, numerical simulations, observations and theoretical analyses. The results indicated that there is an exponential growth relationship between the CO generation rate and the coal temperature, and the critical temperature for rapid oxidation of coal samples is between 70 and 80 °C. The 31,115 working face has complicated air leakage from the working face and ground surface and the goaf of this coal seam. The surface air converges to the return corner through the mining fissure of overburden and 2–2 coal goaf, and the air leakage of the working face flows out from the return roadway through the goaf. The gas leakage in the overlying goaf and the oxidation of residual coal are the main sources of CO in the return corner. The CO generated during the coal mining process and the CO generated by the trackless rubber-tired vehicle operation will increase the CO concentration in the return corner to varying degrees. Under the effect of multi-source air leakage, CO from the overlying goaf and the residual coal in the goaf of this coal seam are migrated to the air return side of the goaf, resulting in the accumulation of CO in the return corner, and both of them have a linear positive correlation with the CO concentration in the return corner. The results of the study have scientific guidance for the control of air leakage and the prevention of CO excess in the goaf.

Z‐scheme Heterojunction Photocatalyst Based on Lanthanum Single‐Atom Anchored on Black Phosphorus for Regulating Surface Active Sites, therefore Enhancing Photocatalytic CO2 Reduction with ≈100% CO Selectivity

AbstractThe advent of Z‐scheme heterojunction makes it possible to improve the CO2 photoreduction efficiency of photocatalyst significantly. However, the reasonable construction of heterojunction and study of the photocatalytic mechanism remains a major challenge. Here, the Z‐scheme heterojunction photocatalyst (BP:La/InVO4:La) based on La single atom anchored on black phosphorus for photocatalytic CO2 reduction with ≈100% CO selectivity is successfully constructed. The CO generation rate of BP:La/5‐InVO4:La is ≈7.9 and 4.9 times higher than black phosphorus and InVO4, respectively. The results of X‐ray photoelectron spectroscopy, photoluminescence, and density functional theory indicate that the BP:La/InVO4:La belongs to the Z‐scheme heterojunction, and the La single atom plays multiple roles such as regulating surface active sites, promoting CO2 absorption, and increasing O defects, which can further contribute to the improvement of photocatalytic performance. The enhanced selectivity of the Z‐scheme heterojunction is further demonstrated by calculating the rate‐determining steps and selectivity‐determining steps. The results are expected to provide unique ideas for the rational design of rare earth composite photocatalyst.

Upscaling studies for efficiently electric-driven CO2 reduction to CO in ionic liquid-based electrolytes

Electric-driven CO2 reduction to high value-added chemicals is a potential way to solve the carbon emissions. However, the current studies on CO2 electroreduction (CO2ER) are mainly focused on design and preparation of novel electrocatalysts and electrolytes. The large-scale of CO2ER is puzzled in the serious hydrogen evolution reaction (HER) in aqueous electrolytes and inferior reaction stability in an enlarged CO2 electrolyzer. Ionic liquids (ILs) as electrolytes have opened great opportunities for CO2ER due to their unique advantages. Herein, a large-scale CO2ER device containing an upscaling modified H-type flow cell using IL-based electrolytes (UHFC-IL) with the largest electrode active area of 495 cm2 was established for CO2ER studies. The influences of key operating parameters, such as compositions of IL-based electrolytes, electrolytes velocity, CO2 gas flow rate and cell voltage on CO2ER performance were systematically investigated. A high CO2ER performance under the optimum operating conditions achieves 83.9% Faraday Efficiency (FE) for CO with a reaction current of 6.32 A, suppressing HER to only 2% FE. After 10 hr continuous operation, the CO selectivity in IL-based electrolytes is 51.3% higher than that in 0.1 M KHCO3 aqueous electrolytes, which maintains excellent stability with a high CO generation rate of 1.7 L hr-1. In addition, the mechanism of CO2ER to CO boosted by IL-based electrolytes in UHFC-IL was proposed. This study provides experimental parameters and guidance for future research on the amplification process of CO2ER.

Black phosphorus/Bi19Br3S27 van der Waals heterojunctions ensure the supply of activated hydrogen for effective CO2 photoreduction

Photocatalytic CO2 reduction (PCC) into solar fuels has been identified as a green avenue for carbon emission reduction. The reactions are usually restricted by the competitive hydrogen production reactions so that the acquisition and utilization of activated hydrogen (H*) in photocatalytic CO2 reduction are hard to guarantee. Herein, heterojunction engineering, regarding amendatory H* supply and balancing hydrogen production reactions simultaneously, for enhancing PCC is achieved by fabricating black phosphorus (BP) nanosheets supported on Bi19Br3S27 nanorods (BP/BBS). Density functional theory calculations united with experimental researches confirm the charge transfer conforms to S-scheme mechanism, which guarantee the efficient separation of photogenerated carriers to facilitate CO2 photoreduction. Free energy analysis reveals the formation of BP/BBS heterojunction changes the active sites from BBS to BP, which decrease the rate-limiting H* formation step from 1.94 (on BBS) to 1.13 eV (BP/BBS heterojunction), ensuring the supply of activated H* for PCC. We found that the heat of the PCC is conducive to dominant protonation of CO2 not H* desorption, which can greatly improve the reduction efficiency of CO2. As a result, the optimized BP/BBS heterojunction achieves an enhanced generation rate of solar fuels in liquid or gas-solid phase system with CO generation rate of 395.7 and 35.4 μmol g−1catalyst, respectively. This work provides an efficient strategy to achieve the supply of activated H* for PCC and other photochemical process.

Ni/support-CaO bifunctional combined materials for integrated CO2 capture and reverse water-gas shift reaction: Influence of different supports

Integrated CO2 capture and utilisation (ICCU) is a promising strategy for restricting carbon emissions and achieving carbon neutrality. Bifunctional combined materials (BCMs), containing adsorbents and active catalysts, are widely applied in this process. Producing syngas via reverse water–gas shift reaction (RWGS) and integrating with Fischer-Tropsch (F-T) synthesis is an attractive and valuable CO2 utilisation route. This work investigated a series of Ni/support-CaO BCMs (supports = ZrO2, TiO2, CeO2 and Al2O3) for the integrated CO2 capture and RWGS (ICCU-RWGS) process. The Ni/support-CaO BCMs were prepared by physically mixing various metal oxide supports loaded Ni with sol–gel derived CaO. The ICCU-RWGS performance (CO2 conversion, CO yield and CO generation rate) of these BCMs followed the order during tested conditions (550–750 °C): Ni/CeO2-CaO > Ni/TiO2-CaO > Ni/ZrO2-CaO > Ni/Al2O3-CaO. A comprehensive characterisation of Ni/support materials showed that Ni/CeO2 had the characteristics of stronger basicity, optimal Ni dispersion and improved NiO reducibility, which led to the outperforming ICCU-RWGS activity over Ni/CeO2-CaO (e.g. 56.1% CO2 conversion, 2.68 mmol g−1 CO yield and ∼100% CO selectivity at 650 °C). Furthermore, the Ni/CeO2-CaO BCM showed a stable, yet, self-optimising catalytic performance during the cyclic ICCU-RWGS reaction over 20 cycles. The TEM characterisation suggested that was ascribed to the volume expansion and shrinkage of CaO in the cyclic adsorption–desorption altering the distance between the adsorbent and Ni/CeO2, resulting in an enhanced CO2 conversion during the cycle.