Photocatalysts For CO2 Reduction Research Articles

Two-Dimensional BiOCl Nanosheet-Encapsulated Cu2O Octahedra: p-n Junction Photocatalysts for Efficient Visible Light Driven CO2-To-CH4 Conversion.

Cu2O has attracted significant attention as a potential photocatalyst for CO2 reduction. However, its practical use is limited by rapid charge recombination, insufficient catalytic sites, and poor stability. In this study, we report a facile synthesis of Cu2O@BiOCl core-shell hybrids with a well-defined shape of Cu2O and a two-dimensional nanosheet structure of BiOCl. The strategic selection of BiOCl nanosheet promotes charge separation efficiency via the formation of interfacial p-n junction and provides the active site for the CO2 reduction leading to enhanced photocatalytic CO2-to-CH4 conversion efficiency. In addition, the core-shell hybrids also showed improved stability against photocorrosion of Cu2O. These findings highlight the potential of Cu2O@BiOCl core-shell hybrids as robust and efficient photocatalysts for sustainable fuel production.

G-C3N4 S-Scheme Homojunction through Van der Waals Interface Regulation by Intrinsic Polymerization Tailoring for Enhanced Photocatalytic H2 Evolution and CO2 Reduction.

The effective S-scheme homojunction relies on the precise regulation of band structure and construction of advantaged charge migration interfaces. Here, the electronic structural properties of g-C3N4 were modulated through meticulous polymerization of self-assembled supramolecular precursors. Experimental and DFT results indicate that both the intrinsic bandgap and surface electronic characteristics were adjusted, leading to the formation of an in-situ reconstructed homojunction interface facilitated by intrinsic van der Waals forces. The homojunction catalyst, composed of g-C3N4 nanodots and ultra-thin g-C3N4 nanoflakes, exhibited a significant S-scheme carrier separation mechanism, which enhances the utilization of electrons and holes. Consequently, under AM 1.5 light irradiation (~100 mW/cm2), the g-C3N4 homojunction photocatalyst achieved a remarkable hydrogen evolution rate of 580 μmol h-1. Furthermore, a reversed CH4 selectivity in CO2 reduction was observed, yielding 80.30 μmol g-1 h-1 with a selectivity of 96.86 %, in contrast to the performance of bulk g-C3N4, which produced only 2.22 μmol g-1 h-1 with the 15.69 % CH4 selectivity. These findings not only highlight the significant potential of the g-C3N4 homojunction photocatalyst for hydrogen production and CO2 reduction but also propose a superior and effective strategy for optimizing the structural properties of g-C3N4, which are crucial for the design of photocatalytic reactions.

CS bonds mediated rapid charge transfer in hm-C4N3/CdS heterostructure for efficient photocatalytic CO2 reduction.

The quest for stable and high-performance photocatalysts is pivotal in advancing the field of photocatalytic CO2 reduction. Traditional single-component semiconductors are often impeded by their inability to concurrently achieve a broad light absorption spectrum, efficient separation of photogenerated charge carriers, and enduring stability, thereby constraining their photocatalytic efficacy. In this study, we introduce an innovative hm-C4N3/CdS heterojunction that broadens the light absorption spectrum and significantly enhances the separation efficiency of photogenerated charge carriers. Notably, this type-II heterojunction design effectively curbs the photocorrosion of CdS, and the CS bonds within the structure expedite electron transfer. Under irradiation, the photocatalyst exhibits a marked increase in activity and stability, yielding CO and CH4 at rates of 67.5μmol g-1h-1 and 7.4μmol g-1h-1, respectively. This work provides valuable insights for promoting efficient and stable photocatalyst for CO2 reduction.

Cr-MOF composited with facet-engineered bimetallic alloys for inducing photocatalytic conversion of CO2 to C2H4.

The design of efficient photocatalysts is crucial for photocatalytic CO2 reduction. This study developed photocatalysts based on MIL-101(Cr) composited with a facet-engineered Pt/Pd nanoalloy (PPNA). Photocatalytic performance evaluations show that MIL-101(Cr) loaded with PPNA exposing {111} facets, namely M-A(111), exhibits a CO2 to C2H4 conversion rate of 9.5 μmol g-1 h-1 in addition to the CO and CH4, whereas M-A(100) with PPNA exposing {100} facets gives CO2 conversion rates of 33.2 for CO and 9.3 μmol g-1 h-1 for CH4 without C2H4. In situ FT-IR revealed that M-A(111) can readily form C2 intermediates during the reaction. This work offers a strategy for the design of photocatalysts for CO2 reduction to C2H4.

Visible-Light-Driven CO₂ Reduction Using Imidazole-Based Metal-Organic Frameworks as Heterogeneous Photocatalysts.

The development of robust, efficient, and cost-effective heterogeneous photocatalysts for visible light-driven CO2 reduction continues to be a significant challenge in the quest for sustainable energy solutions. As a result, increasing attention is being directed towards the exploration of high-performance photocatalysts capable of converting CO2 into chemical feedstocks. Imidazolate Frameworks Potsdam (IFPs)can be a promising candidate for CO2 photoreduction due to their ease of synthesis, use of low-cost, earth-abundant metals, and high chemical and thermal stability. Herein, we report the synthesis of Zn(II)- and Co(II)-based IFPs, specifically IFP-1(Zn) and IFP-5(Co), for photocatalytic CO2 reduction. Moreover, we demonstrate the enhanced photocatalytic activity of redox-innocent Zn-based IFP-1 by partially substituting Zn(II) with redox-active Co(II) in IFP-1(Zn), resulting in the formation of a bimetallic photocatalyst, IFP-1(Zn/Co). The IFP-1(Zn/Co) exhibited significantly improved CO evolution (637 μmol g-1 in 1 hour), compared to the pristine IFP-1(Zn) (29 μmol g-1). Among all the prepared photocatalysts, IFP-5(Co) outperformed both the systems, achieving a CO evolution of 1174 μmol g-1 within 1 hour, due to the presence of catalytic cobalt sites. In addition, through the combination of photophysical and electrochemical studies, along with DFT calculations, we have proposed a plausible mechanism for the photocatalytic CO2 reduction.

Molecular Heterogeneous Photocatalysts for Visible-Light-Driven CO2 Reduction.

Photoreduction of CO2 to high-value chemical fuels presents an effective strategy to reduce reliance on fossil fuels and mitigate climate change. The development of a photocatalyst characterized by superior activity, high selectivity, and good stability is a critical issue for PCR. Molecular heterogeneous photocatalytic systems integrate the advantages of both homogeneous and heterogeneous catalysts, creating a synergistic enhancement effect that increases photocatalytic performance. This review summarizes recent advancements in molecular heterogeneous photocatalysts for CO2 reduction. Much of the discussion focuses on the types of molecular heterogeneous photocatalysts, and their photocatalytic performance in CO2 reduction is summarized. The synthesis strategies for molecular heterogeneous photocatalysts are thoroughly discussed. Finally, the challenges and future prospects of molecular heterogeneous photocatalysts for PCR are addressed.

Theoretical investigations of hydroxyl-functionalized iron-doped phthalocyanine photocatalyst for efficient CO2 reduction to methanol and methane

Theoretical investigations of hydroxyl-functionalized iron-doped phthalocyanine photocatalyst for efficient CO2 reduction to methanol and methane

Interwoven Porous Pristine Cobalt-Based Metal-Organic Framework as an Efficient Photocatalyst for CO2 Reduction.

As a desired utilization of the conversion of CO2 into valuable carbon fuel production under solar energy, it remains challenging due to the lack of efficient catalysts. Herein, a 3D interpenetrating metal-organic framework of [Co(Tipa)(HCOO)2(H2O)]·H2O (Co-Tipa) with 1D open channel is solvothermally synthesized using a semi-flexible ligand (Tipa = tri-(4-(1H-imidazol-1-yl)-phenyl)amine). The tridentate bridge ligand-oriented periodicity Co-Tipa MOF is combined with ruthenium-based photosensitizers under mild reaction conditions to form an efficient nonhomogeneous co-catalyst for photocatalytic CO2 reduction reaction (CO2RR). As a crystalline MOFs catalyst, the CO production rate, selectivity, and the quantum yield under visible light irradiation offer outstanding performance for the synergistic advantages of structural feature, metal center, and organic ligand. The stability and reusability of the Co-Tipa co-catalyst in the reaction system are profited from the robust 3D entangled framework. The mechanism of how to enhance CO2RR performance for the Co-Tipa is assisted in illustration through density functional theory (DFT) calculations. By leveraging the unique structural properties of entangled MOFs, this study offers innovative approaches for the development of more effective and s Co-Tipa catalysts that can selectively CO2 into valuable chemicals and fuels.

Regulating electrons transfer through Pd-O-Bi bridges for boosting photocatalytic CO2 reduction

The photocatalytic efficiency of bismuth-based metal-organic framework (Bi-MOF) is extremely restricted by the rapid recombination of photogenerated electron-hole pairs, which reduce the number of electrons involved in the photocatalytic reduction reaction. Constructing precise interfacial bond bridges between metal nanoparticles (NPs) and MOFs has emerged as an effective strategy to address the above-mentioned issues, promoting the electrons transfer. Herein, this study improves the sluggish dynamics of photogenerated charge in Bi-MOF by inducing the Pd-O-Bi bond bridges at the interface on a Pd NPs-decorated Bi-MOF (Pd/Bi-MOF) nanosheets. This phenomenon results in an interaction between Pd NPs and the Bi-MOF support. And Pd-O-Bi bond bridges provide the fast electron transfer channels, triggering the directional migration of photogenerated electrons from Pd to Bi node, then enhancing the spatial separation of photogenerated electron-hole pairs, finally facilitating overall photocatalytic CO2 reduction. The presence of these bond bridges leads to higher enhancement in CO production for Pd/Bi-MOF nanosheets compared to the Bi-MOF nanosheets under visible light irradiation after 4.5 h. This research demonstrates the importance of interfacial bond bridges and provides a reasonable guide to design efficient photocatalyst for reduction of CO2 to CO.

Novel Single Perovskite Material for Visible-Light Photocatalytic CO2 Reduction via Joint Experimental and DFT Study.

Developing advanced and economically viable technologies for the capture and utilization of carbon dioxide (CO2) is crucial for sustainable energy production from fossil fuels. Converting CO2 into valuable chemicals and fuels is a promising approach to mitigate atmospheric CO2 levels. Among various methods, photocatalytic reduction stands out for its potential to reduce emissions and produce useful products. Here, novel perovskite ZnMoFeO3 (ZMFO) nanosheets are presented as promising semiconductor photocatalysts for CO2 reduction. Experimental results show that ZMFO has a narrow bandgap, exceptional visible light response, large specific surface area, high crystallinity, and various surface-active sites, leading to an impressive photocatalytic CO2 reduction activity of 24.87 µmolg-1h-1 and strong stability. Theoretical calculations reveal that CO2 conversion into CO and CH4 on the ZMFO surface follows formaldehyde and carbine pathways. This study provides significant insights into designing innovative perovskite oxide-based photocatalysts for economical and efficient CO2 reduction systems.

Synergistic effects of Cu7S4@Cu2O core-shell photocatalyst and S-scheme heterojunction in photocatalytic CO2 reduction

In this study, a Cu7S4@Cu2O core-shell S-scheme heterojunction photocatalyst was synthesized via in-situ sulfurization of Cu2O, aimed at enhancing the photocatalytic reduction of CO2 to CO under UV–visible light. Both experimental investigations and Density Functional Theory (DFT) calculations confirmed the S-scheme charge transfer mechanism between the Cu7S4 shell and Cu2O core. The tightly bonded Cu7S4 shell effectively facilitates the separation of photogenerated charge carriers by promoting electron migration from the Cu2O core to the Cu7S4 shell, while significantly improving the photocorrosion resistance of Cu2O. As a result, the Cu7S4@Cu2O catalyst demonstrated superior cycling stability with a CO production rate of 6.19 μmol∙g−1∙h−1. The CO2 photocatalytic reduction mechanism was further elucidated using in-situ infrared spectroscopy, offering critical insights into charge transfer processes. This work provides an approach to the design of highly efficient and stable core-shell S-scheme heterojunction photocatalysts for CO2 reduction.

Pb-N Chemically Anchors CsPbBr3 on 1D Porous Tubular g-C3N4 for Enhanced Photocatalytic CO2 Reduction.

Halide perovskite CsPbBr3 (CPB) quantum dots (QDs) are considered as a promising candidate for solar-driven CO2 conversion for their unique optoelectronic properties and suitable band structure. However, the CO2 conversion efficiency of pristine CsPbBr3 quantum dots is severely limited due to their rapid electron-hole pair recombination and insufficient active sites. In this study, by immobilizing CPB QDs onto one-dimensional (1D) porous tubular g-C3N4 (TCN), an effective 0D/1D CPB@TCN heterojunction photocatalyst for CO2 reduction is fabricated. Density functional theory (DFT) calculations combined with experimental studies demonstrate that CPB QDs are uniformly anchored on the surface of TCN through Pb-N chemical bonding, resulting in efficient separation and transfer of photogenerated carriers in CPB@TCN photocatalysts. The resultant CPB@TCN photocatalysts exhibit significantly enhanced photocatalytic activity for CO2 reduction with the highest conversion rate of 22.62 μmol·g-1·h-1, which is 5.33-times higher than that of pristine CPB QDs. This work unveils the interfacial bonding mechanism of CPB@TCN heterojunction through Pb-N chemical bond, which provides new insights for the development perovskite-based heterojunction photocatalysts.

Efficient UV-Vis-NIR Responsive CO2 Reduction Photocatalyst with Black Pinecone-Shaped Carbon Nitride Loaded with Lanthanum Oxide.

Photothermal catalysis combines the advantages of photocatalysis and thermal activation, which provides a new research angle for CO2 catalytic reduction. In this study, Black carbon nitride with a three-dimensional (3D) pinecone-shaped structure (BPCN) was prepared by a simple solvothermal method using melamine as a precursor without the aid of a template. Lanthanum oxide doping on the BPCN catalysts (BPCN-La) was achieved by ultrasonic impregnation. This unique pinecone-shaped structure consists of self-assembled and interlaced carbon nitride rods (by SEM). The lanthanum element was distributed on the surface of the CN framework in the form of La2O3 (by XPS). The chemical structures of the samples were characterized by solid-state 13C nuclear magnetic resonance (13C NMR) and elaborated by density functional theory (DFT) analysis. This black carbon nitride expanded the light absorption band edge into the near-infrared (NIR) (300-1400 nm, by UV-vis absorption spectra) and had excellent photothermal conversion activity. La atom doping can significantly boost photogenerated electron excitation (by photocurrent test) and promote carrier separation and transfer (by PL). Upon incorporation of La atoms into BPCN, the highest occupied molecular orbital (HOMO) orbital is more concentrated on the oxygen atoms of La2O3. BPCN-La considerably narrowed the band gap width, exhibited an exceptional photothermal effect, and provided a large surface area, which significantly enhanced the photocatalytic reduction of CO2 reactions. The yields of CO reached 58.2 and 104.9 μmol·h-1·g-1 for BPCN and BPCN-La, respectively, with GCN as the control (6.3 μmol·h-1·g-1). Theoretical reaction pathways and selectivity for the photoreduction of CO2 on BPCN and BPCN-La were studied by DFT simulation. This work provides a new vision for the design of photothermal synergistic without extra-thermal input and full spectral response photocatalysts with high efficiency.

Self-Assembly Synthesis of Oxygen and Sulfur Co-Doped Porous Graphitic Carbon Nitride Nanosheets for Boosting CO2 Photoreduction.

Graphitic carbon nitride (CN) has garnered considerable attention in the field of visible-light CO2 photoreduction, but its efficiency remains limited by the intrinsic π-conjugated skeleton. Here, O and S were co-doped CN (O, S/CN) by a facile "hydrolysis + calcination" approach to modulate the physicochemical and electronic structure. Distinctive from S doped CN (SCN), O, S/CN owned porous layer structure with several nanosheets and less SO4 2- groups on the surface. The amount of heteroatom-doping was achieved by changing the hydrothermal temperature. The optimum O, S/CN-80 achieved moderate CO production rate of 1.29 μmol g-1 h-1, which was 3.79 times as much as SCN (0.34 μmol g-1 h-1). The O and most S atoms were substitutionally doped and the effect of S doped state on the improved efficiency of CO generation in O, S/CN was also explored based on the theoretical calculations. This work provides an inspiration to develop efficient dual-doped CN photocatalysts for photocatalytic CO2 reduction.

Engineering Co Single Atoms in Ultrathin BiOCl Nanosheets for Boosted CO2 Photoreduction

AbstractDespite the development of a range of photocatalysts for CO2 reduction, the practical applications are significantly limited by low conversion efficiencies and their reliance on sacrificial agents, which are rooted in thermodynamic and kinetic challenges related to CO2 conversion. Here, the engineering of Co single atoms in ultrathin single‐crystal BiOCl nanosheets for boosted photocatalytic CO2 reduction is reported. The engineering of Co atoms modulates the distribution of photogenerated charges at the catalyst surface, controlling key surface reaction dynamics and suppressing surface electron‐hole recombination. This modulation also improves light absorption and enhances CO2 adsorption and activation, leading to more efficient surface reactions. Notably, CO2 is stably adsorbed onto the (001) face of BiOCl through a Bi‐O‐C(= O)‐Co‐O coordination unit, which lowers the activation energy for CO2 reduction and reduces the formation energy of COOH− intermediates. As a result, the BiOCl photocatalysts achieve a CO formation rate of 183.9 µmol g−1 h−1, when irradiated with a 300 W Xe lamp without cocatalysts or sacrificial agents. It represents an ≈13‐fold increase compared to that of pristine BiOCl, and surpasses most reported Bi‐based photocatalysts to date. Current work provides valuable insights into engineering of single atoms for developing advanced CO2‐reduction photocatalysts.

Noble‐Metal‐Free Modified TiO2 Nanotube Arrays (TNTAs) for Efficient Photocatalytic Reduction of CO2 to CO Under Visible Light

AbstractIn the past decades, TiO2 nanotube arrays (TNTAs) have gained a great attention as a durable photocatalyst for CO2 reduction due to their unique properties. TNTAs have been widely modified with noble metals for increasing their absorption of visible light and limiting their associated rapid electron‐hole recombination rate. However, these metals are extremely expensive, which limits their practical applications in the fields of energy and environment. In this study, three noble‐metal‐free materials of graphitic carbon nitrides, metal–organic framework, and reduced graphene oxide were used for modifying pure TNTAs through a simple drying‐deposition method. The modified TNTAs samples were characterized by X‐ray diffraction, Fourier transform infrared, field emission scanning electron microscopy and energy‐dispersive X‐ray spectroscopy analyses for approving successful synthesis of these nanocomposites. Finally, the modified TNTAs nanocomposites were investigated for their ability in converting the CO2 gas to CO under visible light. However, the TNTAs modified with graphitic carbon nitrides displayed the highest CO productions of 27551 µmol m−2 which represents 16% enhancement compared to that of pure TNTAs (23871 µmol m−2). The enhanced CO2 photoreduction performance of modified TNTAs is attributed to promoted light absorption, increased surface area, and improved electrical conductivity.

Enhancing CO2 photoreduction efficiency with MXene-modified ZnO@Co3O4 double heterojunction

The photocatalytic reduction of CO2 into energy carriers holds significant industrial appeal, but achieving this process kinetically remains challenging due to the lack of well-designed catalysts. This study presents a novel 2D/3D nanostructured photocatalyst, developed by attaching a few-layer Ti3C2 MXene to polyethylenimine (PEI)-modified ZnO@CO3O4 nanocages, which are derived from a bimetallic zinc-cobalt ZIF. The resulting Mx-PEI-ZnO@Co3O4 catalyst achieved impressive yields of CO and CH4 at 594.37 and 42.67 μmol g−1 h−1, respectively, without the need for sacrificial agents and photosensitizers, and maintained remarkable stability across multiple cycles. These yields represent the highest performance for ZnO-based catalysts to date, with quantum efficiency at 380 nm reached up to 25.06 %. The unique S-scheme and Schottky junctions, along with enhanced CO2 adsorption and hydrogen-bond interactions facilitated by the conductive PEI within the Ti3C2/ZnO/Co3O4 double heterojunctions, effectively inhibit electron-hole recombination and significantly enhance CO2 photoreduction performance. This study underscores the combined benefits of double heterojunction engineering, PEI-functionalized CO2 uptake, and MXene co-catalyst integration within a single system, proposing a new approach for designing highly efficient photocatalysts for solar-driven CO2 reduction in energy-efficient fuel production.

Novel Two-dimensional Tellurophosphates: Visible Light Photocatalysts for Water Splitting and Carbon Dioxide Reduction

Exploring efficient two-dimensional (2D) photocatalysts for solar-driven water splitting into hydrogen and oxygen is crucial for sustainable hydrogen energy production. In this study, we investigated the suitability of novel 2D tellurophosphates M2P2Te6 (M=Mg, Ca, Sr, Ba, Ra) for photocatalytic overall water splitting using density functional theory (DFT) approach. The stability of tellurophosphates was assessed based on formation energies, phonon dispersions, ab initio molecular dynamics, and elastic modulus results. These monolayers have desirable direct bandgaps (∼1.6 – 2.2 eV) for efficient light absorption, and their valence and conduction bands ideally straddle both the oxidation and reduction potential of water along with the ability to reduce CO2 to hydrocarbons or carbonaceous products. Moreover, Gibbs free energies of Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER) of tellurophosphate monolayers are also computed and display that these monolayers are viable photocatalysts under the influence of applied external potential. The tellurophosphates monolayers show strong optical absorption, with an absorption coefficient reaching up to 105 cm-1, across both the visible and UV regions of the solar spectrum, accompanied by high carrier mobility (order of 103 cm2 V-1s-1). The predicted solar-to-hydrogen efficiency of all monolayers exceeds 12%, fulfilling the criteria for commercial and economic viability in solar hydrogen production. The theoretical findings of current study imply that novel 2D tellurophosphate monolayers are promising candidates for optoelectronics, especially as photocatalysts for overall water splitting and CO2 reduction.

Mesoporous C-doped C3N5 as a superior photocatalyst for CO2 reduction

Use of naturally abundant solar light for CO2 reduction is a green pathway to reduce carbon footprint. C3N5 is a promising visible-light photocatalyst with enhanced local electron concentration and more active NN sites compared to g-C3N4. We herein report development of mesoporous C-doped C3N5 through a simple copolymerisation of 3-amino-1,2,4-triazole with trimesic acid via hard-templating method, which demonstrated enhanced light absorption ability and delocalised π-electron density (as evident from density functional theory calculation), resulting in efficient charge transfer to the active surface sites of the photocatalyst. The optimised C-doped mesoporous C3N5 exhibited a superior photocatalytic CO2 reduction activity with the CO evolution of 116.6 µmol·g−1, which is 4-fold and 12-fold times higher than that of C3N5 and g-C3N4 respectively. The enhanced photocatalytic CO2 conversion efficiency can be attributed to the synergetic effects of π-electron modulation by C-doping and enhanced surface-active sites brought by mesoporosity.

Reduction of carbon dioxide to methane and ethanol on the surface of graphyne-like boron nitride (BNyen) monolayer: A DFT study

Recently, scientists have created a novel type of boron nitride material known as BNyen. This material is similar in structure to Graphyne and has a higher N:B ratio than traditional boron nitride due to the addition of boron and nitrogen connecting segments within its units. This material has been studied for its potential as a photocatalyst for reduction of CO2 using DFT approaches. Optical and electronic attributes of BNyen suggest that it has a wider visible-light range and a band gap of 5.69 eV. By adding boron to BNyen, patial distributions of LUMO and HOMO indicate that π network has been extended, resulting in significantly greater photocatalytic efficiency. Upon the adsorption of CO2 on BNyen monolayer, the band gap significantly decreases, indicating a strong interaction between the BNyen and CO2. DFT computations were employed to explore the mechanism of CO2 reduction to a single carbon product catalyzed by BNyen. Based on the ΔG values, the optimized pathway for this reduction is from CO2 to CH4. Additionally, the potential formation of di-carbon products was considered, and based on the free energy values, CH3CH2OH is identified as the final di-carbon product. The Gibbs free energies for potential CO2 reaction pathways on BNyen were calculated, revealing that CO2 can be reduced to CH4 with a low limiting potential of −0.37 V and to CH3CH2OH with a low limiting potential of −0.57 V, both processes being powered by solar energy. In CO2RR, the competing hydrogen evolution reaction (HER) must be considered. The free energy of HER (ΔG = 0.96 eV) is significantly higher than the ΔG of the rate-determining steps for the mono-carbon product (0.37 eV) and the di-carbon product (0.57 eV) on BNyen. Therefore, BNyen effectively suppresses HER during the CO2RR process. This research can serve as a valuable guide for developing novel types of BNyen as appropriate photocatalysts for CO2 reduction reactions (CO2RR).