Photoelectrocatalytic Reduction Of CO2 Research Articles

Photoelectroreduction CO2 to Ethanol Over BiFeO3 with Synergistic Effect of Self‐Polarization and External Electric Field

The exploitation of semiconductor self‐polarization is an effective mean of improving the efficiency of electron utilization. In this work, the synthesis of BiFeO3 (BFO) samples with varying photoelectric properties is achieved by modulating the concentration of KOH. The experimental results reveal that BFO‐4 (4 m KOH) has excellent carrier efficiency. Interestingly enough, the ethanol yield of up to 7.05 μmol cm−2 h−1 in the photoelectrocatalytic process, which is 1.4 times than that of single electrocatalysis. Based on the characterization data, the external electric field forms a multi‐electric field coupling in the BFO (external electric field can enhance the self‐polarization electric field), which enhances charge separation efficiency and facilitates surface reactions, and the CO2 reduction performance is improved. Finally, the free energy in the key step of CC coupling on the surface of BiFeO3 is calculated by DFT. This study offers a valuable reference for the application of ferroelectric materials in the photoelectrocatalytic reduction of CO2 and the design of catalysts for C2+ products.

Building organic-inorganic heterojunction NiCo2O4/h-BN toward artificial photosynthesis—Boron as hole

To convert CO2 and water into organic chemicals via photoelectrocatalytic (PEC) reduction of CO2 under mild conditions is considered to be one of promising methods to address a series of problems like climate change and energy crisis caused by over-emission of CO2. Herein, the organic-inorganic heterojunctions were designed and fabricated by using organic h-BN and inorganic NiCo2O4 as precursors. The optimal NiCo2O4@h-BN-6 heterojunction exhibited impressive performance in CO2 reduction, yielding C2+ chemicals with 100 % selectivity in a rate of 28.5 μM cm−2 h−1. This phenomenon is attributed to the structural feature of three active sites of nitrogen in a unique hexacycle like benzene, which benefit the carbon-carbon coupling among the intermediates. The first observed *N-H species suggest that the N sites can adsorb protons and electrons and convert them into highly active hydrogen atoms. The verification experiments demonstrate that the material will oxidize intermediates to acetic acid where boron atoms are presented as holes in semiconductor. The isotopic labeling experiments of 13CO2 and H218O verified that the products were derived from CO2 and water. The key active intermediates such as *CHO, *=CO, and *COCHO in the synthetic process of C2+ products had been confirmed by operando FTIR spectra and DFT calculations.

Synthesis of isolated ZnO nanorods on introducing g-C3N4 for improved photoelectrocatalytic methanol production by CO2 reduction

The photoelectrocatalytic (PEC) CO2 reduction into fuels has been developed as a prospective approach to resolve the environmental and energy concerns. Herein, a composite catalyst comprising ZnO nanorods dispersed on the g-C3N4 surface (g-C3N4/ZnO) was successfully obtained by simple ZnO seed layer formation and then hydrothermal processes. The synthesized and characterized g-C3N4/ZnO catalytic composite showed 2.8 times enhanced photocurrent density at −1 V applied potential than the bare g-C3N4. The g-C3N4/ZnO catalyst exhibited 2.86 times enhanced the PEC CO2 reduction to methanol than the prepared bare ZnO catalyst. The catalyst’s enhanced the PEC CO2 reduction performance was ascribed to the high surface area, and higher generation and lower recombination of e−/h+ pairs. For the first time, this study showed the enhanced methanol production by the PEC reduction of CO2 over the prepared g-C3N4/ZnO catalytic composite.

Photoelectrocatalytic CO2 Reduction to Formate Using a BiVO4/ZIF‐8 Heterojunction

Converting CO2 into high‐value chemical fuels through green photoelectrocatalytic reaction path is considered as a potential strategy to solve energy and environmental problems. In this work, BiVO4/ZIF‐8 heterojunctions are prepared by in‐situ synthesis of ZIF‐8 nanocrystals with unique pore structure on the surface of BiVO4. The experimental results show that the silkworm pupa‐like BiVO4 is successfully combined with porous ZIF‐8, and the introduction of ZIF‐8 can provide more sites for CO2 capture. The optimal composite ratio of 4:1‐BiVO4/ZIF‐8 showed excellent CO2 reduction activity and the lowest electrochemical transport resistance. In the electrocatalytic system, 4:1‐BiVO4/ZIF‐8 exhibits formate Faraday efficiency of 82.60% at −1.0 V vs. RHE. Furthermore, the Faraday efficiency increases to 91.24% at − 0.9 V vs. RHE in the photoelectrocatalytic system, which is 10.8 times that of pristine BiVO4. The results show that photoelectric synergism can not only reduce energy consumption, but also improve the Faraday efficiency of formate. In addition, the current density did not decrease during 34 h electrolysis, showing long‐term stability. This work highlights the importance of the construction of heterojunction to improve the performance of photoelectrocatalytic CO2 reduction.

Efficient CO2 reduction to C2 products in a Ce-TiO2 photoanode-driven photoelectrocatalysis system using a Bnanometer Cu2O cathode

Excessive emission of CO2 into the atmosphere has caused significant environmental issues. Photoelectrocatalytic (PEC) reduction of CO2 is an effective method that combines the benefits of both photo- and electrocatalysis. This process effectively minimizes CO2 emissions, enhances the efficiency of CO2 reduction, and diminishes energy consumption during the reduction process. In this work, we have successfully developed a photoelectrochemical (PEC) system, integrating a Ce-doped TiO2 film as the photoanode and Cu2O as the dark cathode, in which the 4 % Ce-TiO2 film photoanode demonstrated the best performance. Electrochemical performance data revealed that the Cu2O catalysts, characterized by their octahedral geometry that optimally presents active sites for CO2 reduction, displayed superior activity in converting CO2. Through a straightforward hydrothermal synthesis, we crafted three-dimensional, flower-like TiO2 thin films. The strategic incorporation of cerium into the TiO2 matrix not only enhanced the material's crystallinity but also resulted in a uniform and compact morphology. This modification significantly narrowed the band gap of TiO2, thereby boosting its photocatalytic capabilities. In the system where a 4 % Ce-TiO2 thin film photoanode was used to drive the PEC reduction of CO2, the octahedral Cu2O catalyst demonstrated the highest selectivity for C2 products. This occurred at a reaction voltage of −1.4 V vs. RHE, resulting in a total Faraday efficiency of 67.33 %. Notably, this Faraday efficiency is double the one produced from the electrocatalytic (EC) system. This work demonstrates that the use of a 4 % Ce-TiO2 film as a photoanode is able to solve the photocorrosion problem of the Cu2O catalyst while employing a photovoltaic combination to enhance the selectivity to C2 products.

Leaf-like MSX/TiN heterojunction photocathodes mimicking plant cell – An effective strategy to enhance photoelectrocatalytic carbon dioxide reduction and systematic mechanism investigation

Semiconductors, such as metal oxides and metal sulfides (MSX), are widely investigated as effectively catalytic materials to convert carbon dioxide (CO2) and water into chemicals under simulated solar light. These valuable investigations might address both the energy crisis and climate change in our modern society. Herein, a novel strategy to construct leaf-like heterojunctions of VS-ZnIn2S4/TiN-x is reported. The new semiconductor heterojunctions were then applied to photoelectrocatalytic CO2 reduction, achieving excellent performance (formate formation rate of 1173.2 μM h−1 cm−2) attributed to the plant cell-like morphology and enhanced electron mobility from the heterojunction interfaces to the active sites on the surface. Our findings suggest that titanium nitride (TiN) with good conductivity can improve the photoelectrocatalytic ability of MSX through heterojunction construction. The photocathode VS-ZnIn2S4/TiN-3 exhibits 81.0 % selectivity toward C2 products by optimizing the material structure and reaction conditions. According to the systematic investigation of operando Fourier transform infrared (FTIR) spectra, common intermediates such as *COO−, *COOH, *CO, *CHO, *COCHO, and *COCH3 reported in the literature were carefully verified. Among these, the carbene specie serve as the key intermediate responsible for generating other intermediates and resulting in all products.

Photoelectrocatalytic CO2 Reduction to Methanol by Molecular Self-Assemblies Confined in Covalent Polymer Networks.

Inspired by the porous structures of photosynthetic organelles, we report here a new type of photoelectrode based on a standalone macroporous conjugated polymer network (MCN) that converts sunlight into high-energy electrons for CO2 reduction to CH3OH. The MCN provides supramolecular cavities with sufficient functional groups that control the structures of photocatalytic assemblies, which circumvents the geometric limitations of traditional inorganic counterparts. Stabilized interfacial contact between MCN and photocatalysts is achieved by strong chemical linkages throughout the network. Solar irradiation of MCN with a cobalt-based catalyst generates highly reducing electrons for the reduction of CO2 to CH3OH at a conversion efficiency of 70%. Production of CH3OH sustains for at least 100 h, with a small decrease in yield rates. Scaling up the photoelectrode from 1 to 100 cm2 results in photocurrent generation stabilized at 0.25 A and continuous CH3OH production at a conversion efficiency of 85%, demonstrating the scalability and high performances.

Sunlight-promoted CO2 electroreduction with staggered p-n heterojunction by indium-doped bismuth 3D nanoflower structure on oxidized copper foam as self-standing photoelectric cathode over a wide potential window

Exploiting suitable photocathodes to achieve high photocurrent and long-term endurance is still a great challenge in photoelectrocatalytic CO2 reduction (PEC CO2) reactions. Herein, an In-doped Bi2O3 decorated oxidized copper foam (CBIO/CF) self-standing photoelectric cathode is well designed by the self-assembly process without an externally added binder. Via sunlight-promoted strategy, CBIO/CF with a unique 3D hierarchical nanoflower structure displays a superior faradaic efficiency of 90.0 % towards HCOOH over a wide potential window from −0.87 ∼ −1.17 VRHE and reaches 97.8 % at −0.87 VRHE with a partial current density of 14.41 mA cm−2. The in-situ Fourier transform infrared spectroscopy (FTIR) analysis demonstrates the abundant oxygen defects induced by In doping boost CBIO/CF absorbing substantive intermediate species related with formate generations, and porous structure accelerating mass transportation. Moreover, the well-designed staggered p-n heterojunctions of Cu2O and In-doped Bi2O3 on the surface of catalysts favor the generation and separation of electron/hole pairs and contribute to the photocatalytic reduction of CO2 under a bias voltage. This work paves the way for rational regulation of self-supporting photoelectrode for PEC CO2 to HCOOH with suitable conduction band valence bands and high performance and stability.

Single-atom nickel sites boosting Si nanowires for photoelectrocatalytic CO2 conversion with nearly 100% selectivity.

It is a challenge to design a photocathode with well-defined active sites for efficient photoelectrocatalytic CO2 reduction. Herein, single-atom Ni sites are integrated into Si nanowires to develop a novel photocathode, denoted as Ni-NC/Si. The photocathode demonstrates a stable faradaic efficiency for CO production, approaching nearly 100% at -0.6 V vs. RHE. The introduction of single-atom Ni sites provides sufficient active sites for CO2 reduction, thereby improving the selectivity towards CO formation.

Porous two-dimensional CuSe@BiOI isotype heterojunction with highly exposed (1 0 2) facets for efficient photoelectrocatalytic CO2 reduction and photodetection

Using photoelectrochemical technology to construct efficient photoelectric materials has aroused extensive research interest. In this study, we propose a two-dimensional porous CuSe@BiOI isotype heterojunction photocathode for CO2 reduction to formic acid. The heterojunction was constructed by the epitaxial growth of high-quality oriented BiOI nanosheets onto the porous CuSe framework. The CuSe framework as a template to ensure the formation of the (102) facets of BiOI and the isotropic charge transport characteristics of the (102) surface greatly improve the efficiency of charge separation and transfer. This CuSe@BiOI isotype heterojunction electrode can efficiently reduce CO2 to formic acid with a selectivity of up to 80.5 % in 0.5 M potassium bicarbonate aqueous solution. Meanwhile,the performance of the photodetector based on CuSe@BiOI heterostructure is 6.97 × 1011 Jones and a response rate of 87.13 mA W−1. This finding provides a new approach to designing stable heterojunction photoelectrocatalysts with isotropy.

Enhanced photo-electro catalytic CO2 conversion using transition metal doped TiO2 nanoparticles

The Fe, Co, and Ni-doped TiO2 were synthesised by sol–gel process, and the nanomaterials were coated on electrodes through a slurry with Nafion. This study aims to use prepared nanoparticles of Fe, Co, and Ni-doped TiO2 to enhance the photo-electrocatalytic conversion of CO2. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Fourier-transform infrared spectroscopy (FTIR), and electrochemical analyses were utilized to characterise the doped and undoped TiO2 nanoparticles. Transmission electron microscopy (TEM) studies revealed that the nanomaterials had an average size below 20 nm. Tauc plot analysis for optical absorption studies shown a reduction in band gap when doped with Fe, Co and Ni, with the most significant decrease observed for Fe-doped TiO2, following the order Fe < Co < Ni. Electrochemical CO2 conversion efficiencies were investigated through cyclic voltammetry (CV) curves, electrochemical impedance spectroscopy (ESI), and linear sweep voltammetry (LSV) studies. The results were analysed based on various scan rates and photo exposure, indicating superior performance for Fe-TiO2, aligning with the observed band gap trends. Gas chromatography (GC) analysis of the reduction products revealed the generation of hydrocarbons, with Fe-TiO2 exhibiting the most favourable outcomes. This research provides valuable insights into tailoring TiO2 nanoparticles for efficient photo-electro catalytic reduction of CO2.

In situ fabrication of 2D Bi/Bi2O2CO3 nanosheets anchored on Bi substrate for highly-efficient photoelectrocatalytic CO2 reduction to formate

Utilizing photoelectrocatalysis for the CO2 conversion into value-added chemicals presents a promising approach for alleviating energy-environmental crisis, but the current catalysts encounter the limitations of electron transfer efficiency, activity and stability. Herein, we in situ construct Bi/Bi2O2CO3 composite film with nanosheets anchored on Bi substrate to optimize reaction kinetics, and effectively enhance the separation and transport efficiencies of photogenerated carriers. Our findings reveal that the formate Faraday efficiency of 92.68 % at −0.95 V (vs. RHE) for photoelectrocatalytic CO2 reduction over Bi/Bi2O2CO3 film is much higher obviously than 84 % of electrocatalytic CO2 reduction reaches, and there is no significant decrease within 10 h of activity test. Besides, the highest applied bias photon-to-current efficiency and cathode energy efficiency can achieve 1.19 % and 61 %, respectively, indicating the superior energy utilization of the catalyst. Finally, a reasonable electron transfer mechanism for the enhanced photoelectrocatalytic CO2 reduction over Bi/Bi2O2CO3 film is proposed and clarified based on the spectral characterizations and density functional theory calculations. This work should provide a novel perspective for the design and research of Bi-based photocathodes.

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

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

Triazine-COF@Silicon nanowire mimicking plant leaf to enhance photoelectrocatalytic CO2 reduction to C2+ chemicals

Triazine-COF@Silicon nanowire mimicking plant leaf to enhance photoelectrocatalytic CO2 reduction to C2+ chemicals

Photoelectrothermocatalytic reduction of CO2 to glycol via Cu2S/MoS2-Vs octahedral heterostructure with synergistic mechanism

The defects and interface engineering are efficient approaches to adjust the physical and chemical properties of nanomaterials to enhance catalytic performance. In this study, we report a new MOFs-driven porous Cu2S/MoS2-Vs octahedral semiconductor with heterostructure and photothermal effect. The introduction of sulfur vacancies directly improves the adsorption performance of CO2, and the formation of heterostructure significantly increases the charge transfer rate. The C-penetrating material obtained from MOFs not only acts as an octahedral skeleton support, but also gives photothermal effects under photoelectric conditions. The formation rate of sole C2 products in photoelectrocatalytic CO2 reduction by using Cu2S/MoS2-Vs heterostructure is up to 52 μM·h−1·cm−2 equal to the total electron transfer rate of 541 μM·h−1·cm−2. The carbene mechanism and reaction pathways were proposed and verified by 13CO2 isotopic labelling and operando Fourier transform infrared (FT-IR) spectra. The important intermediates of *CO2−, *CO, *CHO and *CHO-CHO were identified by operando FT-IR spectra. In the comparative experiments, the photothermal electrons are beneficial to C2 products. DFT calculations indicate that the presence of S vacancies (Vs) reduces the energy barrier for product generation.

In Situ Preparation of Mo:BiVO4 Photoanodes Coupled with BiOBr Cathode for Efficient Photoelectrocatalytic CO2 Reduction Performance

Photoanode‐driven photoelectrocatalytic (PEC) reduction of CO2 is an ideal way for solving problems such as the greenhouse effect and environmental crisis. In this study, a one‐step hydrothermal method is successfully used for the preparation of BiVO4 films doped with different mass fractions of Mo. In the results, it is shown that when Mo is doped at 1.5 wt%, photocurrent densities of up to 4.11 mA cm−2 are obtained, 3.36 times greater than those of undoped BiVO4, and there is a marked cathodic shifting of water oxidation reaction initiation potential. Subsequently, coupling it with the BiOBr nanosheet cathode, the generated CH3OH rate reaches 45.67 μmol L−1 h−1 cm−2 at a low applied voltage of 1.2 VRHE, with a Faraday efficiency of 60.68% for PEC CO2 reduction. This work is important for Bi‐based thin‐film self‐assembly coupled with PEC CO2 systems.

Efficient photoelectrocatalytic reduction of CO2 to formate via Bi-doped InOCl nanosheets

Converting CO2 into useful substances is an important approach to address the challenge of reducing CO2 emissions and combating climate change. Compared with the traditional process, photoelectrocatalytic CO2 reduction has great potential to solve the problem of CO2 emission. In this work, Bi-doped InOCl cathode catalysts were prepared by a two-step calcination process, and they demonstrated efficient catalytic activity for the reduction of CO2 to formate. The inclusion of bismuth (Bi) in InOCl resulted in improved catalytic performance compared to the native InOCl catalyst. Specifically, the highest formate selectivity can be observed at −0.9 V vs RHE with a Faraday efficiency of 89.9% and the product rate of 101.41 μmol h–1cm–2 when the Bi doping amount is 5%, representing approximately 2 and 3 times the values obtained with native InOCl, respectively. The experimental results indicate that Bi doping promotes the formation of {001} crystalline surfaces in InOCl, while increasing the specific surface area and the availability of more active sites for CO2 reduction. This work holds significant potential for further advancements in the field of photoelectrocatalytic reduction of CO2.

Exploiting hot electrons from a plasmon nanohybrid system for the photoelectroreduction of CO2

Plasmonic materials convert light into hot carriers and heat to mediate catalytic transformation. The participation of hot carriers (photocatalysis) remains a subject of vigorous debate, often argued on the basis that carriers have ultrashort lifetime incompatible with drive photochemical processes. This study utilises plasmon hot electrons directly in the photoelectrocatalytic reduction of CO2 to CO via a Ppasmonic nanohybrid. Through the deliberate construction of a plasmonic nanohybrid system comprising NiO/Au/ReI(phen-NH2)(CO)3Cl (phen-NH2 = 1,10-Phenanthrolin-5-amine) that is unstable above 580 K; it was possible to demonstrate hot electrons are the main culprit in CO2 reduction. The engagement of hot electrons in the catalytic process is derived from many approaches that cover the processes in real-time, from ultrafast charge generation and separation to catalysis occurring on the minute scale. Unbiased in situ FTIR spectroscopy confirmed the stepwise reduction of the catalytic system. This, coupled with the low thermal stability of the ReI(phen-NH2)(CO)3Cl complex, explicitly establishes plasmonic hot carriers as the primary contributors to the process. Therefore, mediating catalytic reactions by plasmon hot carriers is feasible and holds promise for further exploration. Plasmonic nanohybrid systems can leverage plasmon’s unique photophysics and capabilities because they expedite the carrier’s lifetime.

Comprehensive-designed graphene-based quaternary nanocomposite and its synergistic effect towards photoelectrocatalytic CO2 reduction under different electrolytes

Research on the electrochemical reduction of CO2 (CO2ER) and photoelectrochemical reduction of CO2 (PEC-CO2R) to produce hydrocarbon fuels using renewable energy sources is gaining significant attention. In this study, we developed a new quaternary-structured catalytic material that has garnered interest in the catalysis industry. The performance of the catalysts was assessed by conducting CO2 reduction tests using different electrolytes to support the interaction between the cathode surface and the final product. The selectivity and activity of the nanocomposites were evaluated based on the Faradaic efficiency (FE). Among all the tested nanocomposites, the CuO-Graphene-ZnFe2O4-TiO2 nanocomposites (CGZFOT NCs) exhibited the highest FE in each test, particularly 44.08 % in the buffer electrolyte with UV light, which facilitated electron transfer for CO2 reduction to methanol. The second highest FE value of 42.2 % was achieved when NaHCO3 was used as the electrolyte under UV light. Notably, both the experimental conditions demonstrated high FE values in the absence of a light source. Furthermore, the presence of protons affects FE (%) values. NaHCO3, for instance, dissociates into Na+ and HCO3–, and acts as a carrier for hydrocarbon ions, enhancing absorption. The buffering capacity of the buffer electrolyte actively reacts with the produced hydroxide, promoting the mass transfer of CO2 gas. This results in a high current density for redox reactions in sodium hydrocarbonate and a buffer electrolyte for all working electrodes (WEs). The choice of electrolyte significantly affects the performance of the catalyst; thus, we compared catalysts using only one electrolyte to determine whether their activity and selectivity are related to the catalyst structure and properties. The Z-scheme charge carrier mechanism of the quaternary CGZFOT NCs offered efficient separation and carrier of electron-hole pairs, and it was also found that the close-parallel interfacial connection led to improved photoelectrochemical CO2 reduction (PEC-CO2R). In addition, we believe that our experiments provide a complete picture of the performance of catalysts in different environments.

Tailoring Interfaces for Enhanced Methanol Production from Photoelectrochemical CO2 Reduction.

Efficient and stable photoelectrochemical reduction of CO2 into highly reduced liquid fuels remains a formidable challenge, which requires an innovative semiconductor/catalyst interface to tackle. In this study, we introduce a strategy involving the fabrication of a silicon micropillar array structure coated with a superhydrophobic fluorinated carbon layer for the photoelectrochemical conversion of CO2 into methanol. The pillars increase the electrode surface area, improve catalyst loading and adhesion without compromising light absorption, and help confine gaseous intermediates near the catalyst surface. The superhydrophobic coating passivates parasitic side reactions and further enhances local accumulation of reaction intermediates. Upon one-electron reduction of the molecular catalyst, the semiconductor-catalyst interface changes from adaptive to buried junctions, providing a sufficient thermodynamic driving force for CO2 reduction. These structures together create a unique microenvironment for effective reduction of CO2 to methanol, leading to a remarkable Faradaic efficiency reaching 20% together with a partial current density of 3.4 mA cm-2, surpassing the previous record based on planar silicon photoelectrodes by a notable factor of 17. This work demonstrates a new pathway for enhancing photoelectrocatalytic CO2 reduction through meticulous interface and microenvironment tailoring and sets a benchmark for both Faradaic efficiency and current density in solar liquid fuel production.