Ultrathin Ti-doped WO₃ nanosheets realizing selective photoreduction of CO₂ to CH₃OH

Li Z., Zeng H., Zeng G., Ru C., Li G., Yan W., Shi Z., Feng S.

Improving proton conductivity and fabricating viable metal-organic frameworks (MOFs) based proton exchange membranes (PEMs) are central issues exploiting electrolyte MOFs. We aim to design multivariate flexibility synergistic strategy to achieve Flexible MOFs (FMOFs) with high conductivity at a wide range of humidity. In situ powder X-ray diffraction (PXRD) and temperature-dependent Fourier transform infrared spectra (FT-IR) prove the synergistic self-adaption between dynamic torsion of alkyl sulfonic acid and dynamic breathing of FMOF, forming a continuous hydrogen-bonding networks to maintain high conductivity. Based on the convincing proton conductivity, we construct a series of long-term durable MOF-based PEMs that serve as a bridge between MOF and fuel cell. Consequently, the membrane electrode assembly (MEA) of the flexible PMNS1-40 exhibits a maximum single-cell power density of 34.76 mW cm-2 and hopefully opens doors to evaluate the practical application of proton-conducting MOFs in direct methanol fuel cells.

Guo W., Liu S., Tan X., Wu R., Yan X., Chen C., Zhu Q., Zheng L., Ma J., Zhang J., Huang Y., Sun X., Han B.

We have prepared atomically dispersed Sn catalysts on defective CuO for CO2 electroreduction to methanol. The Faradaic efficiency of methanol could reach 88.6 % with a current density of 67.0 mA cm−2. The catalyst was beneficial for CO2 activation via decreasing the energy barrier of *COOH dissociation to form *CO. The *CO was then bound to the Cu species for further reduction, leading to high selectivity toward methanol.

He J., Wu C., Li Y., Li C.

This work reviews the recent advances of pre-catalysts for CO2 reduction reaction (CO2RR) research. The important factors that may be responsible for the improvement of the CO2RR performance are categorized and a perspective is also presented.

Vo C.H., Mondelli C., Hamedi H., Pérez-Ramírez J., Farooq S., Karimi I.A.

Nguyen H.L., Alzamly A.

Chen T., Liu T., Shen X., Zhang W., Ding T., Wang L., Liu X., Cao L., Zhu W., Li Y., Yao T.

Engineering the electronic properties of catalysts to target intermediate adsorption energy as well as harvest high selectivity represents a promising strategy to design advanced electrocatalysts for efficient CO2 electroreduction. Herein, a synergistically tuning on the electronic structure of the CdSe nanorods is proposed for boosting electrochemical reduction of CO2. The synergy of Ag doping coupled with Se vacancies tuned the electronic structure of the CdSe nanorods, which shows the metalloid characterization and thereby the accelerated electron transfer of CO2 electroreduction. Operando synchrotron radiation Fourier transform infrared spectroscopy and theoretical simulation revealed that the Ag doping and Se vacancies accelerated the CO2 activation process and lowered the energy barrier for the conversion from CO2 to *COOH; as a result, the performance of CO2 electroreduction was enhanced. The as-obtained metalloid Ag-doped CdSe nanorods exhibited a 2.7-fold increment in current density and 1.9-fold Faradaic efficiency of CO than pristine CdSe nanorod.

Navarro-Jaén S., Virginie M., Bonin J., Robert M., Wojcieszak R., Khodakov A.Y.

Carbon dioxide (CO2) is the iconic greenhouse gas and the major factor driving present global climate change, incentivizing its capture and recycling into valuable products and fuels. The 6H+/6e− reduction of CO2 affords CH3OH, a key compound that is a fuel and a platform molecule. In this Review, we compare different routes for CO2 reduction to CH3OH, namely, heterogeneous and homogeneous catalytic hydrogenation, as well as enzymatic catalysis, photocatalysis and electrocatalysis. We describe the leading catalysts and the conditions under which they operate, and then consider their advantages and drawbacks in terms of selectivity, productivity, stability, operating conditions, cost and technical readiness. At present, heterogeneous hydrogenation catalysis and electrocatalysis have the greatest promise for large-scale CO2 reduction to CH3OH. The availability and price of sustainable electricity appear to be essential prerequisites for efficient CH3OH synthesis. This Review identifies competitive advantages and drawbacks of heterogeneous and homogeneous catalytic hydrogenation, as well as enzymatic catalysis, photocatalysis and electrocatalysis, for CO2 reduction to methanol.

Ma J., Mao K., Low J., Wang Z., Xi D., Zhang W., Ju H., Qi Z., Long R., Wu X., Song L., Xiong Y.

Photoelectrochemical (PEC) conversion of methane (CH4 ) has been extensively explored for the production of value-added chemicals, yet remains a great challenge in high selectivity toward C2+ products. Herein, we report the optimization of the reactivity of hydroxyl radicals (. OH) on WO3 via facet tuning to achieve efficient ethylene glycol production from PEC CH4 conversion. A combination of materials simulation and radicals trapping test provides insight into the reactivity of . OH on different facets of WO3 , showing the highest reactivity of surface-bound . OH on {010} facets. As such, the WO3 with the highest {010} facet ratio exhibits a superior PEC CH4 conversion efficiency, reaching an ethylene glycol production rate of 0.47 μmol cm-2  h-1 . Based on in situ characterization, the methanol, which could be attacked by reactive . OH to form hydroxymethyl radicals, is confirmed to be the main intermediate for the production of ethylene glycol. Our finding is expected to provide new insight for the design of active and selective catalysts toward PEC CH4 conversion.

Shao W., Wang S., Zhu J., Li X., Jiao X., Pan Y., Sun Y., Xie Y.

Sluggish separation and migration kinetics of the photogenerated carriers account for the low-efficiency of CO2 photoreduction into CH4. Design and construction two-dimensional (2D) in-plane heterostructures demonstrate to be an appealing approach to address above obstacles. Herein, we fabricate 2D in-plane heterostructured Ag2S-In2S3 atomic layers via an ion-exchange strategy. Photoluminescence spectra, time-resolved photoluminescence spectra, and photoelectrochemical measurements firmly affirm the optimized carrier dynamics of the In2S3 atomic layers after the introduction of in-plane heterostructure. In-situ Fourier transform infrared spectroscopy spectra and density functional theory (DFT) calculations disclose the in-plane heterostructure contributes to CO2 activation and modulates the adsorption strength of CO* intermediates to facilitate the formation of CHO* intermediates, which are further protonated to CH4. In consequence, the in-plane heterostructure achieves the CH4 evolution rate of 20 µmol·g−1·h−1, about 16.7 times higher than that of the In2S3 atomic layers. In short, this work proves construction of in-plane heterostructures as a promising method for obtaining high-efficiency CO2-to-CH4 photoconversion properties.

Zhu S., Li X., Jiao X., Shao W., Li L., Zu X., Hu J., Zhu J., Yan W., Wang C., Sun Y., Xie Y.

Selective CO2 photoreduction into a high-energy-density C2 product is still challenging. Here, charge-polarized metal pair sites are designed to trigger C-C coupling through manipulating asymmetric charge distribution on the reduction intermediates. Taking the synthetic partially reduced Co3O4 nanosheets as an example, theoretical calculations unveil the asymmetric charge distribution on surface cobalt sites. The formed charge-polarized cobalt pair sites not only donate electrons to CO2 molecules but also accelerate the coupling of asymmetric COOH* intermediates through lowering the energy barrier from 0.680 to 0.240 eV, affirmed by quasi in situ X-ray photoelectron spectroscopy and Gibbs free energy calculations. Also, the electron-rich cobalt sites strengthen their interaction with O of the HOOC-CH2O* intermediate, which favors the C-O bond cleavage and hence facilitates the rate-limiting CH3COOH desorption process. The partially reduced Co3O4 nanosheets achieve 92.5% selectivity of CH3COOH in simulated air, while the CO2-to-CH3COOH conversion ratio is 2.75%, obviously higher than that in pure CO2.

Li X., Wang S., Li L., Zu X., Sun Y., Xie Y.

ConspectusExcessive use of fossil fuels has not only led to energy shortage but also caused serious environmental pollution problems due to the massive emissions of industrial waste gas. As the main component of industrial waste gas, CO2 molecules can also be utilized as an important raw material for renewable fuels. Thus, the effective capture and conversion of CO2 has been considered one of the best potential strategies to mitigate the energy crisis and lower the greenhouse effect simultaneously.In this case, CO2 electroreduction to high-value-added chemicals provides an available approach to accomplish this important goal. Nonetheless, the CO2 molecule is extremely stable with a high dissociation energy. With regard to the traditional electrocatalytic systems, there are three main factors that hinder their practical applications: (i) sluggish carrier transport dynamics; (ii) high energy barrier for CO2 activation; (iii) poor product selectivity. Therefore, solving these three crucial problems is the key to the development of efficient electrocatalytic CO2 reduction systems.Considering that the CO2 molecule is a typical Lewis acid with a high first ionization energy and electronic affinity, electron-rich catalysts could help to activate the CO2 molecule and improve the conversion efficiency. In view of this, atomically thin two-dimensional electrocatalysts, benefiting from their significantly increased density of states near the Fermi level, have great potential to effectively accelerate the dynamics of electron transport. Moreover, their high fraction of surface active sites and enhanced local charge density could remarkably reduce the energy barrier for CO2 activation. Furthermore, their modulated electronic structure could alter the catalytic reaction pathway and improve the product selectivity. Meanwhile, the concise two-dimensional configuration facilitates in situ characterization as well as the establishment and simulation of theoretical models, which helps to reveal the mechanism of electrocatalytic CO2 reduction, thereby speeding up the development of CO2 conversion technology.In this Account, we summarize recent progress in tailoring the electronic structure of atomically thin two-dimensional electrocatalysts by different methods. Meanwhile, we highlight the structure-property relationship between the electronic structure regulation and the catalytic activity/product selectivity of atomically thin two-dimensional electrocatalysts, and discuss the underlying fundamental mechanism with the aid of in situ characterization techniques. Finally, we discuss the major challenges and opportunities for the future development of CO2 electroreduction. It is expected that this Account will help researchers to better understand CO2 electroreduction and guide better design of high-performance electrocatalytic systems.

Li X., Xin Z., Xia S., Gao X., Tung C., Wu L.

The protocol of artificial photosynthesis using semiconductor nanocrystals shines light on green, facile and low-cost small molecule activation to produce solar fuels and value-added chemicals.

Li Y., Wang S., Wang X., He Y., Wang Q., Li Y., Li M., Yang G., Yi J., Lin H., Huang D., Li L., Chen H., Ye J.

Developing unique single atoms as active sites is vitally important to boosting the efficiency of photocatalytic CO2 reduction, but directly atomizing metal particles and simultaneously adjusting the configuration of individual atoms remain challenging. Herein, we demonstrate a facile strategy at a relatively low temperature (500 °C) to access the in situ metal atomization and coordination adjustment via the thermo-driven gaseous acid. Using this strategy, the pyrolytic gaseous acid (HCl) from NH4Cl could downsize the large metal particles into corresponding ions, which subsequently anchored onto the surface defects of a nitrogen-rich carbon (NC) matrix. Additionally, the low-temperature treatment-induced C═O motifs within the interlayer of NC could bond with the discrete Fe sites in a perpendicular direction and finally create stabilized Fe-N4O species with high valence status (Fe3+) on the shallow surface of the NC matrix. It was found that the Fe-N4O species can achieve a highly efficient CO2 conversion when accepting energetic electrons from both homogeneous and heterogeneous photocatalysts. The optimized sample achieves a maximum turnover number (TON) of 1494 within 1 h in CO generation with a high selectivity of 86.7% as well as excellent stability. Experimental and theoretical results unravel that high valence Fe sites in Fe-N4O species can promote the adsorption of CO2 and lower the formation barrier of key intermediate COOH* compared with the traditional Fe-N4 moiety with lower chemical valence. Our discovery provides new points of view in the construction of more efficient single-atom cocatalysts by considering the optimization of the atomic configuration for high-performance CO2 photoreduction.

Shit S.C., Shown I., Paul R., Chen K., Mondal J., Chen L.

Recent advances in nanotechnology, especially the development of integrated nanostructured materials, have offered unprecedented opportunities for photocatalytic CO2 reduction.

Kong T., Jiang Y., Xiong Y.

This tutorial review elucidates how to design catalytically active sites for efficient and highly selective photocatalytic reduction of CO2 by learning from conventional CO2 hydrogenation and syngas conversion.

Chen R., Wu Q., Luo J., Zu X., Zhu S., Sun Y.

Syrek K., Wierzbicka E., Zych M., Piecha D., Szczerba M., Sołtys-Mróz M., Kapusta-Kołodziej J., Sulka G.D.

Zheng L., Wei Y., Wang C., Liu H., Li L., Huang M., Huang Y., Fan L., Wu J.

Gu X., Lin S., Qi K., Yan Y., Li R., Popkov V., Almjasheva O.

WO3-based photocatalysis has garnered significant interest among researchers worldwide. With a band gap ranging between 2.5 and 2.7 eV, WO3 emerges as a promising candidate material for photocatalytic applications due to its excellent electrochemical properties, high stability, and ability to enhance photoactivity in various crystalline forms. Noteworthy features of WO3 include exceptional stability in harsh conditions, cost-effectiveness, high hole drift velocity, and a tunable energy gap. In this comprehensive review, we first explore the diverse morphologies of WO3 obtained through different preparation methods. Secondly, we investigate the photocatalytic efficiency of WO3-based composites. Thirdly, strategies for identifying optimal photocatalysts, such as crystal plane optimization, doping, surface modification, and hetero/homojunction fabrication, are summarized. Additionally, the integration of carbon-based composites to form type-II, Z-scheme, and S-scheme configurations is detailed. The review delves into various applications of WO3, including pollutant degradation, CO2 reduction, and water splitting, providing an in-depth analysis. Furthermore, the challenges and prospects associated with WO3-based photocatalysts are highlighted, along with discussions on methods to enhance their performance. This review aims to inspire academics to innovate concepts for advancing sustainable energy production in the next generation

Fu C., Wan Z., Yang X., Zhang J., Zhang Z.

We summarized the design strategies for photocatalysts to enhance CO2 reduction and accepted pathways for selective photocatalytic CO2 conversion.

Deng S., Wang N., Zhu Y., Thummavichai K.

Nowadays, the excessive use of fossil fuels has led to a global energy shortage and exacerbated the greenhouse effect.

Du C., Sheng J., Zhong F., He Y., Guro V.P., Sun Y., Dong F.

Photocatalytic CO2 conversion into high-value chemicals is becoming an increasingly promising avenue of research in the quest for sustainable carbon resource utilization. Particularly, compounds with two or more carbons (C2+) have higher added value than methane, carbon monoxide, or formate, which are typically the major products of CO2 reduction. In this review, we present a detailed account of recent advancements in the field of photocatalytic CO2 conversion, with a specific focus on the synthesis of multi-carbon oxygenates. We systematically introduce the rational design of photocatalysts with high effectivity and selectivity, which follows a methodical inside-to-outside order. These strategies consider various aspects of photocatalyst optimization, from the core structure to the surface properties. Meanwhile, we delve into an in-depth analysis of the underlying catalytic mechanisms, particularly emphasizing the C-C coupling and multi-electron-coupled proton transfer processes. Lastly, we examine the prospects and challenges in developing photocatalysts for CO2 conversion, providing valuable insights for researchers and practitioners. This review aims to serve as a valuable resource for those seeking to design advanced catalysts for efficient photocatalytic CO2 reduction.

Cheng M., Cao N., Wang Z., Wang K., Pu T., Li Y., Sun T., Yue X., Ni W., Dai W., He Y., Shi Y., Zhang P., Zhu Y., Xie P.

Sun X., Wang D., Wu W., Zhao X., Zhang X., Wang B., Rong X., Wu G., Wang X.

Liu H., Zhou H., Yang L., Pan Y., Zhao X., Wang F., Fang R., Li Y.

Solar-driven CO2 reduction to CO production is often hampered by the kinetically sluggish water photooxidation and fast recombination of photocarriers. Herein, we report a photoredox system of CO2 reduction coupled with biomass-based amines oxidation. Double-shelled CdS nanocages (CdS DSNC) are synthesized by a successive etching‑sulfuration strategy, which delivers impressive CO and difurfurylamine yields of 1226.4 and 5526.5 μmol·g−1·h−1, respectively. Mechanism studies uncover that the double-shelled structure endows CdS DSNC with high accessibility of active sites and short transfer distance for photocarriers. Besides, furfurylamine serves as both the electron donor and the capturer of CO2, thus boosting the photoredox performance.

Maximov Anton L., Beletskaya Irina P.

Development of the "methanol" economy may be a way to establish the new chemistry under decarbonization conditions. Methanol here is used as a raw material for production of a wide range of chemicals, conventionally obtained from oil. The key process for the "methanol" economy is the reduction of CO2, which, along with renewable energy, is the main carbon-containing resource in the low-carbon industry. This review summarizes recent data on the main approaches to methanol production from CO2: catalytic hydrogenation of CO2 with hydrogen on heterogeneous or homogeneous catalysts; electrochemical reduction of CO2 to methanol; and CO2 conversion using photocatalysis. The main advantages and disadvantages of each method, the mechanisms of CO2 conversion taking into account the features of each type of catalysis, and the main approaches to the efficient catalysts are discussed.The bibliography includes 542 references.

Li Y., Zhu J., Zhao N., Ma G., Liu B., Xu J., Tayebee R.

Benzimidazoles are potential compounds in the development of various important drugs and their anti-cancer properties against cancerous glioma cells. In this study, an efficient and environmental friendly photocatalyst is proposed for the synthesis of a range of 2-substituted benzimidazoles through condensation of aromatic aldehydes with o-phenylenediamine by the mediation of Ti-WO3 nanophotocatalyst under irradiation of a commercial green laser. To characterize Ti-WO3 several techniques such as FT-IR, DRS, XRD, XPS, TEM, and FE-SEM are employed to elucidate the structure and physicochemical properties of this nanomaterial. In addition, the reusability test confirmed excellent recovery and reproducibility of the nanophotocatalyst. Furthermore, an in-vitro cellular toxicity was performed by using Ti-WO3 nanoparticles against the U87MG human glioma cancer cell line through MTT assay. The results showed a clear reduction in cell viability, which confirmed the cytotoxicity of Ti-WO3 against the performed cell line.

Yan X., Zhang J., Hao G., Jiang W., Di J.

AbstractArtificial photosynthesis can convert carbon dioxide into high value‐added chemicals. However, due to the poor charge separation efficiency and CO2 activation ability, the conversion efficiency of photocatalytic CO2 reduction is greatly restricted. Ultrathin 2D photocatalyst emerges as an alternative to realize the higher CO2 reduction performance. In this review, the basic principle of CO2 photoreduction is introduced, and the types, advantages, and advances of 2D photocatalysts are reviewed in detail including metal oxides, metal chalcogenides, bismuth‐based materials, MXene, metal‐organic framework, and metal‐free materials. Subsequently, the tactics for improving the performance of 2D photocatalysts are introduced in detail via the surface atomic configuration and electronic state tuning such as component tuning, crystal facet control, defect engineering, element doping, cocatalyst modification, polarization, and strain engineering. Finally, the concluding remarks and future development of 2D photocatalysts in CO2 reduction are prospected.

Wang S., Huang L., Peng Y., Chen L.

Photocatalytic CO2 reduction has been regarded as a practical and theoretical strategy to tackle the environmental and energy problems, yet remains a great challenge in conversion efficiency. In this work, Cu-doped WO3 square nanoplates were fabricated through a one-step hydrothermal process and employed as catalysts for CO2 photoreduction. It was revealed that Cu doping in WO3 led to a more negative conduction band (CB) position, decreased bandgap energy, enhanced visible-light absorption capability, and high separation and transfer efficiency of photoinduced charge carriers. As a result, the Cu-doped WO3 displays a superior photocatalytic performance for CO2 photoreduction into CH4/CO as compared to the pure WO3. The best Cu–WO3 sample achieves CO and CH4 formation rates of 3.23 and 1.63 μmol‧g−1‧h−1, which are 25 and 27-folds higher than those of pure WO3, respectively. This work may propose a valid approach to engineer WO3 nanoplates for boosting CO2 photocatalytic reduction under visible-light irradiation.

He Q., Sheng B., Zhu K., Zhou Y., Qiao S., Wang Z., Song L.