Efficient CO2 Reduction Research Articles

A local acidic environment at the copper/molten salt interface enabling the efficient CO2 to CO conversion

The electrochemical reactions highly rely on the chemical environments, however, this phenomenon remains poorly understood in nonaqueous electrolyte. Herein, we study the effect of the electrode chemical environments on the electrochemical reduction of CO2 in molten carbonate. Using a Cu foam electrode, an acidic (CO2-rich) environment is created to achieve the efficient direct reduction of CO2 rather than the indirect reduction of CO32–. The acidic environment promotes a selective CO production thermodynamically, achieving a high CO current efficiency of 99 % at a current density of 779–1039 mA cm−2 at 700 °C. The Cu foam electrode works stably over 100 h at 260 mA cm−2 with an overpotential of 304 mV. This work reveals the role of the local chemical environment at the electrode/molten salt interface in governing the product selectivity and energy consumption, which is helpful for designing efficient high-temperature CO2 electrolyzers.

Integration of Plasmonic Ag(I) Clusters and Fe(II) Porphyrinates into Metal-Organic Frameworks for Efficient Photocatalytic CO2 Reduction Coupling with Photosynthesis of Pure H2O2.

Efficient photocatalytic CO2 reduction coupled with the photosynthesis of pure H2O2 is a challenging and significant task. Herein, using classical CO2 photoreductionsite iron porphyrinate as the linker, Ag(I)clusters were spatially separated and evenly distributed within a new metal-organic framework (MOF), namely Ag27TPyP-Fe. With water as electron donors, Ag27TPyP-Fe exhibited remarkable performances in artificial photosynthetic overall reaction with CO yield of 36.5 μmol g-1 h-1 and ca. 100% selectivity, as well as H2O2 evolution rate of 35.9 μmol g-1 h-1. Since H2O2 in the liquid phase can be more readily separated from the gaseous products of CO2 photoreduction, high-purity H2O2 with a concentration up to 0.1 mM was obtained. Confirmed by theoretical calculations and the established energy level diagram, the reductive iron(II) porphyrinates and oxidative Ag(I) clusters within an integrated framework functioned synergistically to achieve artificial photosynthesis. Furthermore, photoluminescence spectroscopy and photoelectrochemical measurements revealed that the robust connection of Ag(I) clusters and iron porphyrinate ligands facilitated efficient charge separation and rapid electron transfer, thereby enhancing the photocatalytic activity.

Clustering‐Resistant Cu Single Atoms on Porous Au Nanoparticles Supported by TiO2 for Sustainable Photoconversion of CO2 into CH4

AbstractPhotocatalysts based on single atoms (SAs) modification can lead to unprecedented reactivity with recent advances. However, the deactivation of SAs‐modified photocatalysts remains a critical challenge in the field of photocatalytic CO2 reduction. In this study, we unveil the detrimental effect of CO intermediates on Cu single atoms (Cu‐SAs) during photocatalytic CO2 reduction, leading to clustering and deactivation on TiO2. To address this, we developed a novel Cu‐SAs anchored on Au porous nanoparticles (CuAu‐SAPNPs‐TiO2) via a vectored etching approach. This system not only enhances CH4 production with a rate of 748.8 μmol ⋅ g−1 ⋅ h−1 and 93.1 % selectivity but also mitigates Cu‐SAs clustering, maintaining stability over 7 days. This sustained high performance, despite the exceptionally high efficiency and selectivity in CH4 production, highlights the CuAu‐SAPNPs‐TiO2 overarching superior photocatalytic properties. Consequently, this work underscores the potential of tailored SAs‐based systems for efficient and durable CO2 reduction by reshaping surface adsorption dynamics and optimizing the thermodynamic behavior of the SAs.

Clustering-Resistant Cu Single Atoms on Porous Au Nanoparticles Supported by TiO2 for Sustainable Photoconversion of CO2 into CH4.

Photocatalysts based on single atoms (SAs) modification can lead to unprecedented reactivity with recent advances. However, the deactivation of SAs-modified photocatalysts remains a critical challenge in the field of photocatalytic CO2 reduction. In this study, we unveil the detrimental effect of CO intermediates on Cu single atoms (Cu-SAs) during photocatalytic CO2 reduction, leading to clustering and deactivation on TiO2. To address this, we developed a novel Cu-SAs anchored on Au porous nanoparticles (CuAu-SAPNPs-TiO2) via a vectored etching approach. This system not only enhances CH4 production with a rate of 748.8 μmol ⋅ g-1 ⋅ h-1 and 93.1 % selectivity but also mitigates Cu-SAs clustering, maintaining stability over 7 days. This sustained high performance, despite the exceptionally high efficiency and selectivity in CH4 production, highlights the CuAu-SAPNPs-TiO2 overarching superior photocatalytic properties. Consequently, this work underscores the potential of tailored SAs-based systems for efficient and durable CO2 reduction by reshaping surface adsorption dynamics and optimizing the thermodynamic behavior of the SAs.

Bimetallic NiCu catalyst derived from spent MOF adsorbent for efficient photocatalytic CO2 reduction

The metal–organic frameworks (MOFs) rich in porous structures and their derivatives have been widely developed and applied to heavy metal adsorption. However, little attention has been paid to the subsequent treatment and reutilization of spent MOFs adsorbents. A potential feasible strategy is to develop MOFs-derived bimetallic catalysts for energy conversion. Herein, a bimetallic Ni-Cu2O-Cu/C nanocomposite (Ni-Cu/C) derived from spent Cu-based MOFs (CuBTC) adsorbents was fabricated and applied to improve the performance of photocatalytic CO2 reduction. The results demonstrate that Ni doping could improve the charge transfer dynamics. The synthesized Ni-Cu/C catalyst exhibits a high CO yield (12.45 μmol g−1 h−1) in the pure water system in the absence of other photosensitizers and sacrificial agents, which is 2.05 folds higher compared to Cu/C. The CO2 conversion selectivity of the synthesized Ni-Cu/C catalyst reaches up to 99.0%. The mechanism of photocatalytic CO2 reduction reaction was further investigated by in-situ experiments and density functional theory calculation. The in-situ FT-IR characterization show that photogenerated electrons could effectively adsorb CO2 to produce CO2− and optimize *CO immediate. This work not only emphasizes the unique design of bimetallic catalyst derived from spent MOFs adsorbent, but also contributes a feasible solution to its reutilization for enhanced CO2 conversion.

Nickel phthalocyanine anchored onto N-doped biochar for efficient electrocatalytic carbon dioxide reduction

Molecular catalysts have been receiving extensive attention due to their explicit, designable, easily modifiable molecular structures and tunable catalytic active sites, which exhibit elegant electrocatalytic performance in electrocatalytic carbon dioxide reduction reactions. However, the susceptibility to aggregation due to strong intermolecular π-π interactions among the metal bipyridines, phthalocyanines and porphyrins among the molecular catalysts limits their catalytic performance. Herein, an active catalyst nickel phthalocyanine anchored N-doped ball milled biochar (NiPc/N-BMBC) was developed with highly enriched pore structure and high surface area for electrocatalytic CO2 reduction reaction. On the nanoscale, NiPc molecules were uniformly anchored on N-BMBC to enhance the dispersion, exposing sufficient catalytic active sites. Concretely, the catalyst NiPc/N-BMBC exhibited extraordinary performance in the electrolytic conversion of CO2 reduction reaction, with a Faredaic efficiency of CO (FECO) > 70 % at an overpotential (−0.75 to −0.95 V vs. RHE) and a high CO partial current density (jCO) of 96 mA cm−2 at −1.0 V vs. RHE, which were much higher than that of NiPc (24 %, 38 mA cm−2) and N-BMBC (9 %, 2 mA cm−2). This work provides a new insight in the structural design of carbon-based electrocatalyst for efficient electrocatalytic CO2 reduction reaction.

Engineering Controls for Scaling CO2 Electrolyzers

The electrochemical CO2 reduction (CO2R) to ethylene on copper-based catalysts has garnered significant attention for its potential in sustainable industrial practices. While substantial progress has been achieved in the development of small-scale electrolyzers with geometric areas ranging from 1 to 5 cm2, the imperative to address larger scales for industrial decarbonization necessitates a shift in focus. There are inherent critical risks when scaling a nascent technology like CO2 electrolysis. There can be emergent phenomena observed only at larger scales, that can prevent it from reaching commercialization, such as change in local CO2 concentration, defects in the porous transport layer, and temperature gradients The optimized conditions for operating a 5 cm2 electrolyzer may not work well with a 25 cm2 electrolyzer leading to failures. Therefore, there is a need to develop a systematic way to test for these phenomena to address these challenges to successfully operate a CO2R electrolyzer at an industrially relevant scale. In this work, we highlight the performance of a Cu-based catalyst designed for the selective reduction of CO2 to ethylene across varying scales, ranging from 5 to 100 cm2. This investigation shows the changes in the electrolyzer performance at different scales. Our findings highlight the critical importance of implementing engineering controls to overcome challenges associated with the scaling of electrolyzers. Specifically, we explore the impact of anolyte flow rate, gasket compression, and electrochemical pulsing techniques on maintaining the desired selectivity of the electrocatalyst across different scales. By systematically adjusting these parameters, we demonstrate the ability to mitigate non-linear effects and uphold the efficiency of CO2 reduction to ethylene, even on larger electrode surfaces.This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.

Probing the Activity and Selectivity of Nickel Carboxylethylphosphonate 2D-MOF for the Electrochemical Conversion of CO2 to Syngas

The increasing concentration of CO2 in the atmosphere is alarming for modern society and the reduction of CO2 into valuable products would be a unique solution.1 Metal–organic frameworks (MOFs), constructed from organic linkers interconnected with metal (oxide) nodes, with high porosity and large surface area, have become an emerging class of electrocatalysts for reduction of CO2.2,3 Herein, we report the synthesis and characterization of a two-dimensional nickel metal-organic framework (2D Ni-MOF) with 3-phosphopropionic acid and 4,4-bypyridine as ligands and Ni2+ as the node (figure 1). The electrocatalytic activity of this material is explored for the electrochemical CO2 reduction reaction (CO2RR). An onset potential for the electrochemical reduction CO2 activity of -0.51 V vs RHE was observed which is 70 mV more positive than the HER in Ar-saturated electrolyte suggesting an efficient CO2 reduction. This catalyst showed a high current density of 33.5 mA cm-2 at 1.01 V vs RHE, exhibiting superior performance to most of the MOFs tested so far for CO2 reduction (figure 2a and b). Long term electrolysis at -0.8 V (vs RHE) yielded a current density of ∼10 mA cm-2 with high selectivity towards the formation of CO and H2 with an average production ratio of 30:70%, respectively (figure 2c and d). This new Ni-MOF catalyst retained its crystallinity and morphology after electrolysis as confirmed by powder XRD, HRTEM, FT-IR and Raman spectroscopy, indicating promising stability of the catalyst.Density functional theory (DFT) was employed to calculate adsorption-free energy of the reaction intermediates to identify the active catalytic sites responsible for CO2 reduction in our 2D Ni-MOF structure. Findings show that the catalyst more readily reduces H* to H2 (with a limiting potential of 0.48 eV) than CO2 to COOH* (limiting potential of 0.78 eV). The reaction mechanism upon which this calculation was based begins with the removal of the H2O molecule bound to the Ni (II) site, followed by CO2 adsorption and the two proton-coupled electron transfer steps yielded COOH* and then CO & H2O. The H2O is more strongly adsorbed to the Ni (II) site than CO which closes the mechanistic cycle. Reference 1. M. J. B. Kabeyi and O. A. Olanrewaju, Frontiers in Energy Research, 2022, 9.2. B.-X. Dong, S.-L. Qian, F.-Y. Bu, Y.-C. Wu, L.-G. Feng, Y.-L. Teng, W.-L. Liu and Z.-W. Li, ACS Applied Energy Materials, 2018, 1, 4662-4669.3. J.-X. Wu, S.-Z. Hou, X.-D. Zhang, M. Xu, H.-F. Yang, P.-S. Cao and Z.-Y. Gu, Chemical Science, 2019, 10, 2199-2205. Figure 1

Effect of Electrolyte Composition over CO2 Reduction

The rapid utilization of fossil fuels escorted by an excess of CO2 emissions has led to global energy and environmental crisis. Therefore, the necessity for a clean, renewable and sustainable source of energy is a growing concern for the present and future society. In this regard, economically viable CO2 reduction would be a critical turnover in research, as it has the potential to fulfil a substantial need for clean energy. However, even though many efforts have been done in this field, there is still room for improvements concerning efficiency, material stability, and catalytic enhancement in regard of kinetics and selectivity. Herein, we provide the experimental proof for enhancement of the CO2 reduction efficiency and selectivity from the SEI (semiconductor-electrolyte interface) side through the use of carbonates, borates, sulphates and alkali cations as the electrolyte as well as an overview of the latest developments on Cu2O based PEC CO2 reduction for solar fuel production. Cu2O is a low-cost semiconductor and one of the most promising candidates for PEC CO2RR. However, its stability and performance is still unsatisfactory, thus the CO2 reduction products vary from one investigated system to another, such as: CH3OH, CO, HCOOH, CH3COOH, and CH3CH2OH. Moreover, the instability of Cu2O causes it, to be rarely used for the routine CO2 reduction reaction. In this paper, we use a very facile electrodeposition method, which offers a high level of reproducibility and the possibility of using a new electrode in each experiment, in order to focus our efforts on following the phenomena occurring in the double layer during the photocatalytic run. In this way, we were able to correlate the final CO2RR performance with a reorganization of the cations and anions near the photocatalyst surface. It is shown in the literature that factors such as: carbonate concentration, local pH, the presence of alkali metal cations, the geometry of the anionic group, CO2 solubility, conductivity, as well as pH changes along with the number of H+ in the electrolyte, play a significant role in regulating the partial CO2RR current. In this paper, we would like to shed new light on the influence of the electrolyte composition, cation-anion interaction and local reaction environment around the catalyst on the performance of CO2RR. We found out that the specific interaction between the alkali cation and the anionic group of particular geometry contributes to the formation of a kind of a “rigid layer” within the double diffusion, close to the photocatalyst surface layer, which accounts more for an apparent CO2RR current than the decrease in the finite Warburg element, which is a central key parameter for the diffusion coefficient values. The effectiveness of the strength of the cation-anion interaction in the formation of the “rigid layer” around the photocatalyst surface is found to increase the PEC CO2RR performance. Elucidating this mechanism provides useful information for creating further experimental design and the new pathways for addressing highly efficient PEC CO2RR systems. The authors have noticed a significant knowledge gap in the existing literature, as no prior publications have delved into the concurrent and combined impact of both cations and anions on PEC CO2RR. In this pioneering publication, we present the inaugural investigation of this this intricate phenomenon.

Regulating Local Electron Density of Cyano Sites in Graphitic Nitride Carbon by Giant Internal Electric Field for Efficient CO2 Photoreduction to Hydrocarbons.

Selective photocatalytic CO2 reduction to high-value hydrocarbons using graphitic carbon nitride (g-C3N4) polymer holds great practical significance. Herein, the cyano-functionalized g-C3N4 (CN-g-C3N4) with a high local electron density site is successfully constructed for selective CO2 photoreduction to CH4 and C2H4. Wherein the potent electron-withdrawing cyano group induces a giant internal electric field in CN-g-C3N4, significantly boosting the directional migration of photogenerated electrons and concentrating them nearby. Thereby, a high local electron density site around its cyano group is created. Moreover, this structure can also effectively promote the adsorption and activation of CO2 while firmly anchoring *CO intermediates, facilitating their subsequent hydrogenation and coupling reactions. Consequently, using H2O as a reducing agent, CN-g-C3N4 achieves efficient and selective photocatalytic CO2 reduction to CH4 and C2H4 activity, with maximum rates of 6.64 and 1.35µmol g-1h-1, respectively, 69.3 and 53.8 times higher than bulk g-C3N4 and g-C3N4 nanosheets. In short, this work illustrates the importance of constructing a reduction site with high local electron density for efficient and selective CO2 photoreduction to hydrocarbons.

Enhancing *CO coverage on Sm-Cu2O via 4f-3d orbital hybridization for highly efficient electrochemical CO2 reduction to C2H4

The electrocatalytic conversion of CO2 into valuable chemical feedstocks using renewable electricity offers a compelling strategy for closing the carbon loop. While copper-based materials are effective in catalyzing CO2 to C2+ products, the instability of Cu+ species, which tend to reduce to Cu0 at cathodic potentials during CO2 reduction, poses a significant challenge. Here, we report the development of Sm-Cu2O and investigate the influence of f-d orbital hybridization on the CO2 reduction reaction (CO2RR). Supported by density functional theory (DFT) calculations, our experimental results demonstrate that hybridization between Sm3+ 4f and Cu+ 3d orbitals not only improves the adsorption of *CO intermediates and increases CO coverage to stabilize Cu+ but also facilitates CO2 activation and lowers the energy barriers for CC coupling. Notably, Sm-Cu2O achieves a Faradaic efficiency for C2H4 that is 38% higher than that of undoped Cu2O. Additionally, it sustains its catalytic activity over an extended operational period exceeding 7 h, compared to merely 2 h for the undoped sample. This research highlights the potential of f-d orbital hybridization in enhancing the efficacy of copper-based catalysts for CO2RR, pointing towards a promising direction for the development of durable, high-performance electrocatalysts for sustainable chemical synthesis.

Molten salt construction of core-shell structured S-scheme CuInS2@CoS2 heterojunction to boost charge transfer for efficient photocatalytic CO2 reduction

Molten salt construction of core-shell structured S-scheme CuInS2@CoS2 heterojunction to boost charge transfer for efficient photocatalytic CO2 reduction

Porous Bi Nanosheets Derived from β-Bi2O3 for Efficient Electrocatalytic CO2 Reduction to Formate.

The electrochemical CO2 reduction reaction (ECO2RR) is a promising strategy for converting CO2 into high-value chemical products. However, the synthesis of effective and stable electrocatalysts capable of transforming CO2 into a specified product remains a huge challenge. Herein, we report a template-regulated strategy for the preparation of a Bi2O3-derived nanosheet catalyst with abundant porosity to achieve the expectantly efficient CO2-to-formate conversion. The resultant porous bismuth nanosheet (p-Bi) not only exhibited marked Faradaic efficiency of formate (FEformate), beyond 91% in a broad potential range from -0.75 to -1.1 V in the H-type cell, but also demonstrated an appreciable FEformate of 94% at a high current density of 262 mA cm-2 in the commercially important gas diffusion cell. State-of-the-art X-ray absorption near edge structure spectroscopy (XANES) and theoretical calculation unraveled the distinct formate production performance of the p-Bi catalyst, which was cocontributed by its smaller size, plentiful porous structure, and stronger Bi-O bond, thus accelerating the absorption of CO2 and promoting the subsequent formation of intermediates. This work provides an avenue to fabricate bismuth-based catalysts with high planar and porous morphologies for a broad portfolio of applications.

Modulating the Electrocatalytic CO2-CO Performance by Ag Morphology

Highly selective conversion of CO2 into CO molecules remains a major challenge in electrocatalytic CO2 reduction reactions, and metallic silver-based materials have great potential. However, the selectivity and activity of traditional silver (Ag)-based materials cannot reach the desired level, and the development of new Ag-based materials has become a hot research topic. Here, novel ag-glomerated spore-shaped Ag nanomaterials are reported for the efficient reduction of CO2 to CO. The unique nanostructures endowed with larger specific surface area, and the spore-like dispersed Ag nanoparticles (NPs) have more unsaturated Ag sites, which endowed the catalysts with higher intrinsic activity. Electrochemical tests show that spore-like Ag can obtain a Faraday efficiency (FE) of 95.6% at −1 V vs RHE, which is much higher than that of Ag nanowires (NWs) (73%) and ordinary Ag NPs (83%) synthesized in the same period. By using the three different morphologies of Ag synthesized as a research platform and statistically comparing the FE in the corresponding voltage interval, we obtained the influence of morphology effect on the selectivity of CO product production by electrocatalytic CO2 production over Ag-based catalysts, which can be further used as a guideline for catalyst development.

Enhancing CO2 reduction efficiency with axial oxygen coordinated Ni-N4 active Sites on hierarchical pore N-doped carbon

Enhancing CO2 reduction efficiency with axial oxygen coordinated Ni-N4 active Sites on hierarchical pore N-doped carbon

The interfacial synergistic catalysis effect within Cu/ZrO2 heterogeneous catalyst for highly efficient and selective electrocatalytic reduction of CO2 to CH4

Highly selective production of valuable methane from electrocatalytic CO2 reduction reaction (ECO2RR) is a highly attractive yet particularly challenging route for CO2 utilization. Constructing Cu/metal-oxide (MOx) heterogeneous interface is a feasible strategy for efficient catalyst design, which can realize the electronic control of the surface interface by utilizing the synergistic effect between Cu and metal-oxide. Here we constructed Cu/ZrO2 heterogeneous interface to synthesize a new Cu2+ catalyst. The XPS measurements confirmed that the appropriate ratio of Cu/ZrO2 can effectively stabilize Cu2+ at Cu-O-Zr interface against reduction. The CO temperature-programmed desorption experiments (CO-TPD) showed that the high relative content of Cu2+ in 0.2Cu/ZrO2 can significantly strengthen the adsorption stability of the *CO, which in turn promotes the protonation of the *CO intermediate instead of dimerization, further favoring the generation of methane. The activity data showed the distinctly superior reactivity of 0.2Cu/ZrO2 catalyst, which exhibits an ultra-high faradaic efficiency (FE) of CH4 of 72.0 % and a low FEC2H4 of 2.9 %. This work unravels the valence state and performance relationship of Cu/ZrO2 catalysts and provides a new insight into the electrosynthesis of CH4 as product.

Tree-inspired semiconductor-on-ceramic 2D/1D heterostructure for efficient CO2 photoreduction

Two-dimension nanosheets are ideal photocatalysts for CO2 reduction due to their high exposure of active sites and short charge transfer pathway. However, 2D photocatalysts have a tendency to agglomeration, thus compromising the performance of photocatalytic CO2 reduction. Trees, one of the most important plants for photosynthesis, have a unique “leaf-on-branch” structure. This unique two-dimension/one-dimension (2D/1D) configuration maximizes the adsorption of CO2 molecules and light harvesting. Herein, a tree-inspired semiconductor-on-ceramic 2D/1D heterostructure for efficient photocatalytic CO2 reduction is reported. The cobalt silicate (CoSi) nanosheets (∼0.68 nm) are in situ grown on the surfaces of hydroxyapatite (HAP) nanowires, creating a well-defined 2D/1D hierarchical structure. The vertical alignment of ultrathin CoSi nanosheets on the HAP nanowires effectively suppresses their agglomeration, leading to a large BET surface area (106.45 m2/g) and excellent CO2 adsorption (8.00 cm3 g−1). The results of photoelectrochemical characterization demonstrate that the 2D/1D hierarchical structure is powerful to expedite charge transfer. As a result, the gas generation rate of CO is as high as 28780 μmol g−1 h−1 over the CoSi-on-HAP 2D/1D heterostructure. In addition, the electron transfer mechanism and reaction pathways of CO2 reduction are revealed by in situ irradiated XPS and in situ DRIFT spectra.

Sr(Ti0·3Fe0.7)O3−δ-based perovskite with in-situ exsolved Fe–Ru nanoparticles: A highly stable fuel electrode material for solid oxide electrochemical cells with efficient electrocatalytic CO2 reduction ability and preferential selectivity

The development of solid-oxide cells requires fuel electrodes capable of promoting highly catalytic activities for CO2 electrochemical reduction (CO2R). This study develops a fuel electrode material, Sr(Ti0·3Fe0·63Ru0.07)O3-δ (STFR) perovskite, enhance with in-situ exsolved Fe–Ru nanoparticles (STFR–FeRu), demonstrating excellent electrochemical catalytic activity for CO2R, considerable stability, and high selectivity for CO2 electrolysis. Notably, the study discovered for the first time that STFR–FeRu exhibits significantly enhanced catalytic activity in a CO2-containing atmosphere compares to that in hydrogen-based fuels. At 800 °C and 1.3 V, La0·8Sr0.2Ga0.8Mg0·2O3-δ electrolyte-supported cells with STFR–FeRu fuel electrode, for direct CO2 electrolysis, realizes a current density of 1.77 A cm−2. This current density is 50 % higher than that of H2O electrolysis under the same conditions. Additionally, the cell achieves a current density of 1.54 A cm−2 for CO2–H2O co-electrolysis, with a high CO2 electrolysis selectivity (CO concentration exceeding 60 % in the electrolysis products).

MXene quantum dots decorated g-C3N4/BiOI heterojunction photocatalyst for efficient NO deep oxidation and CO2 reduction

The photocatalytic performance of g-C3N4 is greatly limited by the severe charge recombination due to its s-triazine unit structure. Hence, enhancing the separation of photogenerated carriers is the pivotal factor for high-efficiency photocatalysis of g-C3N4. In this work, we construct a MXene quantum dots (MQDs) decorated BiOI/g-C3N4p-n heterojunction photocatalyst. The interfacial charge separation and transfer are substantially promoted, due to the synergistic effect of the internal electric field (IEF) of BiOI/g-C3N4 heterojunction and strong electron-withdrawing capability of MQDs. Furthermore, the introduction of BiOI with a low band gap and MQDs with large specific areas and rich surface terminals lead to enhanced light absorption and active sites. As a result, the ternary g-C3N4/MQDs/BiOI photocatalyst achieves a much higher NO removal rate of 42.23 % and discharges less NO2 intermediate than the individual and binary ones. Meanwhile, the g-C3N4/MQDs/BiOI photocatalyst also exhibits the most effective CO2 photoreduction, with a CO production rate of 57.8 μmol·g−1·h−1 and a CH4 production rate of 3.6 μmol·g−1·h−1, surpassing all other photocatalysts in this study. In addition, the designed composite photocatalyst shows remarkable stability. The photocatalytic mechanisms are studied by the trapping experiment and in-situ Fourier Transform Infrared (FTIR) Spectra. This work paves a new avenue for enhancing charge separation and thus improving performances of g-C3N4-based photocatalysts by integrating a p-n heterojunction and a co-catalyst, which would accelerate commercial deployment of emerging photocatalysts.

Manipulating Ferroelectric Polarization and Spin Polarization of 2D CuInP2S6 Crystals for Photocatalytic CO2 Reduction.

Manipulating electronic polarizations such as ferroelectric or spin polarizations has recently emerged as an effective strategy for enhancing the efficiency of photocatalytic reactions. This study demonstrates the control of electronic polarizations modulated by ferroelectric and magnetic approaches within a two-dimensional (2D) layered crystal of copper indium thiophosphate (CuInP2S6) to boost the photocatalytic reduction of CO2. We investigate the substantial influence of ferroelectric polarization on the photocatalytic CO2 reduction efficiency, utilizing the ferroelectric-paraelectric phase transition and polarization alignment through electrical poling. Additionally, we explore enhancing the CO2 reduction efficiency by harnessing spin electrons through the synergistic introduction of sulfur vacancies and applying a magnetic field. Several advanced characterization techniques, including piezoresponse force microscopy, ultrafast pump-probe spectroscopy, in situ X-ray absorption spectroscopy, and in situ diffuse reflectance infrared Fourier transformed spectroscopy, are performed to unveil the underlying mechanism of the enhanced photocatalytic CO2 reduction. These findings pave the way for manipulating electronic polarizations regulated through ferroelectric or magnetic modulations in 2D layered materials to advance the efficiency of photocatalytic CO2 reduction.