Photoelectrocatalytic Reduction Research Articles

Photoelectrocatalytic reduction of carbon dioxide to methanol at cuprous oxide foam cathode

Photoelectrocatalytic performance of Cu2O foam electrodes for reduction of CO2 to methanol depends largely on exposed Cu2O{111} facets.

Photoelectrocatalytic reduction of CO2 to methanol over the multi-functionalized TiO2 photocathodes

The photoelectrocatalytic (PEC) reduction of CO2 to chemical fuels was achieved by utilizing the multi-functionalized TiO2 film photocathodes. On the surfaces of TiO2 films, Pd nanoparticles were introduced to catch protons, molecules of Eosin Y disodium salt were embedded to absorb solar energy, and four different amine ligands were immobilized to capture and activate CO2. In the novel PEC cells, multi-functionalized TiO2 and Co-Pi/W:BiVO4 films were served as photocathode and the counter electrode, respectively. It was found that methanol was the major liquid product. Besides, some ethanol and acetone can be detected as well. The maximum formation rate and the highest selectivity of methanol were 43.6μMcm−2h−1 and approximately 100%, respectively. The Faradaic efficiencies of the PEC cells can exceed 1000% with the aid of photoelectrons. The 13CO2 labeling experiments verify that methanol and carbon monoxide are derived from CO2.

Recent progress and perspectives in the photocatalytic CO2 reduction of Ti-oxide-based nanomaterials

The conversion of CO2 with H2O to valuable chemicals and fuels is a new solution to current environmental and energy problems, and the high energy barrier of these reactions can be overcome by the input of solar and electrical energy. However, the reduction efficiencies and selectivities of these reactions are insufficient for practical use, and significant effort and strategy are required to overcome the many obstacles preventing the large-scale application of photocatalytic CO2 reduction. This article reviews recent progress in CO2 reduction using titanium oxide-based materials and various strategic factors for increasing photocatalytic efficiency. This article also highlights non-titanium-oxide catalysts, the photoelectrocatalytic reduction of CO2, and other recent review articles concerning the recycling of CO2 to value-added carbon compounds.

Fabrication of visible-light active Fe2O3-GQDs/NF-TiO2 composite film with highly enhanced photoelectrocatalytic performance

Visible-light active Fe2O3-GQDs/NF-TiO2 composite films were fabricated via sequential electro-deposition and electro-oxidation processes. The prepared photocatalytic films were extensively characterized using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy and X-ray photoelectron spectroscopy (XPS). The results revealed that graphene quantum dots (GQDs) and α-Fe2O3 particles were simultaneously deposited onto the surface of N and F co-doped TiO2 (NF-TiO2) simply using a graphite sheet instead of a Pt sheet as anode in the electro-deposition process. The NF-TiO2 substrate obtained by calcining TiO2 nanotubes (TiO2-NTs) in the presence of NH4F displayed pyramid shapes with dominant (101) facets. Linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) plots indicated that the generation, separation and transfer of photogenerated charges were greatly enhanced on the novel composite. The photocurrent density of Fe2O3-GQDs/NF-TiO2 was 4.2 times that on Fe2O3/TiO2-NTs at 0.5V vs. Ag/AgCl under visible light irradiation. For the photoelectrocatalytic (PEC) reduction of Cr(VI) using Fe2O3-GQDs/NF-TiO2 as photoanode with a Ti sheet as cathode, substantially enhanced activity was achieved due to the combined effect of visible-light-active components (α-Fe2O3 and NF-TiO2) and excellent electron mediator (GQDs). The calculated reduction rate constant was 7 times that obtained on Fe2O3/TiO2-NTs film. Furthermore, both the long-time photocurrent and cyclic PEC reduction of Cr(VI) indicated good stability of the composite film.

Different CdSeTe structure determined photoelectrocatalytic reduction performance for carbon dioxide

CdSeTe nanoparticles (CdSeTe NPs)/TiO2 nanotubes (TiO2 NTs) and CdSeTe nanosheets (CdSeTe NSs)/TiO2 NTs were fabricated by photoelectric deposition method and hydrothermal method, respectively. The band gap of the CdSeTe NPs/TiO2 NTs (1.24eV) is narrower than that of the CdSeTe NSs/TiO2NTs (1.48eV). The photoelectrochemical conversion efficiency of the CdSeTe NPs/TiO2 NTs is 2.72 times larger than that of the CdSeTe NSs/TiO2 NTs, manifesting that the CdSeTe NPs/TiO2 NTs possessed more excellent photocatalytic performance. Furthermore, the current density of electrocatalytic reduction CO2 on the CdSeTe NPs/TiO2 NTs was 2.47 times larger than that of the CdSeTe NSs/TiO2 NTs, showing the excellent electrocatalytic performance of the CdSeTe NPs/TiO2 NTs. The major product methanol was detected in the PEC reduction process on the two as-prepared materials. The yield reached 18.57mmolL−1 after 300min on CdSeTe NPs/TiO2NTs, which is 16 times larger than that of CdSeTe NSs/TiO2 NTs.

One dimensional SnO2 NRs/Fe2O3 NTs with dual synergistic effects for photoelectrocatalytic reduction CO2 into methanol

The hydrothermal method was explored to prepare SnO2 nanorods (SnO2 NRs) with the special faces of (110) and (101) on the surface of Fe2O3 nanotubes (Fe2O3 NTs). According to the SEM and XRD results, the formation process of the hierarchically assembled SnO2 NRs was deduced. The SnO2 NRs/Fe2O3 NTs catalyst that had reached for 120 mins behaved the best photoelectrocatalytic properties. From the view of photocatalytic reduction, the conduction band (−0.75eV vs NHE) is negative enough to drive CO2 reduction, and the valence band (1.82eV) is positive enough to oxidize H2O to generate proton, and then the proton is used for CO2 reduction. From the electrocatalytic reduction point, the net CO2 reduction current density of the composite is 7.48 times that of Fe2O3 NTs at −1.1V, indicating that the electrocatalytic performance of Fe2O3 NTs is greatly enhanced by the introduction of 6-fold branched SnO2 NRs. The predominant reduction product is analyzed by GC was methanol. Herein, two synergistic effects are proved according to the methanol yields, one is the synergistic effect of the photocatalytic and electrocatalytic reduction, the other is the synergistic effect between SnO2 NRs and Fe2O3 NTs. The results indicated that the composite catalyst behaves excellent photoelectrocatalytic activity for CO2 reduction.

Highly enhanced photoelectrocatalytic properties by α-Fe2O3 modified NF-TiO2 pyramids with dominant (101) facets

Visible-light-active Fe2O3/NF-TiO2 film was prepared by depositing α-Fe2O3 nanoparticles onto the surface of pyramid-shaped NF-TiO2 via sequential electro-deposition and electro-anodization processes. NF-TiO2 with dominant (101) facets was obtained via calcining TiO2 nanotubes (TiO2-NTs) in the presence of NH4F. The structural and optical properties were carefully studied by XRD, SEM, HRTEM, XPS and UV-Vis-DRS. Photoelectrochemical measurements, such as linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS) and Mott-Schottky (M-S) plots, were also carried out to investigate the generation, separation and transfer of photogenerated charges. It was found that Fe2O3/NF-TiO2 exhibited the best photoelectrocatalytic (PEC) activity relative to Fe2O3/TiO2-NTs or Fe2O3/N-TiO2. The formation of anatase-rutile heterojunction, wider spectral response, increased photocurrent response and greatly reduced charge transfer resistance, could be positive driving force for the enhanced PEC activity. Simultaneous PEC reduction of Cr(VI) and degradation of phenol were evaluated under visible light using Fe2O3/NF-TiO2 film as photoanode and Ti sheet as cathode. The calculated rate constants for Cr(VI) and phenol were 4.3 and 3.6 times relative to that on Fe2O3/TiO2-NTs, respectively. Good stability was also confirmed in cyclic runs using the optimized photoanode.

Photoelectrocatalytic reduction of CO2 into formic acid using WO3–x/TiO2 film as novel photoanode

A novel WO3–x/TiO2 film as photoanode was synthesized for photoelectrocatalytic (PEC) reduction of CO2 into formic acid (HCOOH). The films prepared by doctor blade method were characterized with X-ray diffractometer (XRD), scanning electron microscope (SEM) and transmission electron microscope (TEM). The existence of oxygen vacancies in the WO3–x was confirmed with an X-ray photoelectron spectroscopy (XPS), and the accurate oxygen index was determined by a modified potentiometric titrimetry method. After 3 h of photoelectrocatalytic reduction, the formic acid yield of the WO3–x/TiO2 film is 872 nmol/cm2, which is 1.83 times that of the WO3/TiO2 film. The results of PEC performance demonstrate that the introduction of WO3–x nanoparticles can improve the charge transfer performance so as to enhance the performance of PEC reduction of CO2 into formic acid.

Photoelectrocatalytic reduction of perchlorate in aqueous solutions over Ag doped TiO2 nanotube arrays

Abstract Photoelectrocatalytic reduction of aqueous perchlorate using Ag nanoparticles loaded TiO2 nanotube arrays (Ag-TNTs) in the presence of a hole scavenger (citric acid, Cit) under UV light irradiation was investigated in this study. TiO2 nanotube arrays (TNTs) were prepared by anodic oxidation and Ag nanoparticles were loaded on TNTs by photodeposition. Ag-TNTs were characterized by X-ray diffraction, scanning electron microscope and X-ray photoelectron spectroscopy. The influences of Ag doping content, photogenerated electron, photogenerated hole, hydroxyl radical, initial pH and applied voltages on photoelectrocatalytic perchlorate reduction were studied and the optimum reaction conditions were determined. Results indicated that Ag-TNTs have the best photoelectrocatalytic activity when the nominal mass ratio of Ag to TiO2 is 0.84%. With an initial perchlorate concentration of 0.001 mM, the perchlorate reduction efficiency can reach 62% in the presence of Cit (0.15 mM) after 6 h reaction (368 ± 0.5 K) at applied voltage of 1.5 V.

ChemInform Abstract: Photocatalytic and Photoelectrocatalytic Reduction of CO2 Using Heterogeneous Catalysts with Controlled Nanostructures

AbstractReview: [130 refs.

Photocatalytic and photoelectrocatalytic reduction of CO2 using heterogeneous catalysts with controlled nanostructures.

The development of efficient artificial photocatalysts and photoelectrocatalysts for the reduction of CO2 with H2O to fuels and chemicals has attracted much attention in recent years. Although the state-of-the-art for the production of fuels or chemicals from CO2 using solar energy is still far from practical consideration, rich knowledge has been accumulated to understand the key factors that determine the catalytic performances. This Feature article highlights recent advances in the photocatalytic and photoelectrocatalytic reduction of CO2 with H2O using heterogeneous semiconductor-based catalysts. The effects of structural aspects of semiconductors, such as crystalline phases, particle sizes, morphologies, exposed facets and heterojunctions, on their catalytic behaviours are discussed. The roles of different types of cocatalysts and the impact of their nanostructures on surface CO2 chemisorption and reduction are also analysed. The present article aims to provide insights into the rational design of efficient heterogeneous catalysts with controlled nanostructures for the photocatalytic and photoelectrocatalytic reduction of CO2 with H2O.

Highly Efficient Photoelectrocatalytic Reduction of Hexavalent Chromium based on the Cascade Energy Transfer towards Using no Semiconducting Photocatalysts

Highly efficient photoelectrocatalytic (PEC) reduction of Cr(VI) has been realized in the absence of semiconducting photocatalysts. In the novel-configuration cell using Ti anode, Pt cathode, Cr(VI), and citric acid, the rate constant of the PEC reduction of Cr(VI) at a bias of 1.5V was almost 3 times than that in the conventional-configuration cell using ITO/TiO2 anode, Ti cathode, Cr(VI), and citric acid. It was mostly because the citric acid, Ti anode, and Cr(VI) formed an energy-relay cascade structure, in which the photogenerated electrons in the citric acid were transferred to the positively biased Ti and then from anode to Cr(VI), leading to the very efficient Cr(VI) reduction. We develop a simple PEC method to reduce Cr(VI) over the Ti anode sensitized by photoexcited organic dye in no need of metal oxide photocatalysts, which can be considered as an important advance towards the cost-effective, environmentally friendly treatment of waste water.

Co-doped MoS2 NPs with matched energy band and low overpotential high efficiently convert CO2 to methanol

Co-doped MoS2 NPs (30nm in diameter) was prepared by hydrothermal method and used for photoelectrocatalytic reduction of CO2. Compared with MoS2, the novel catalyst Co-doped MoS2 NPs obtained the valence band and conduction band locating at 0.89V and −0.52V, which leaded to the high efficient photocatalytic reduction performance. In the aspects of electrocatalysis, resistance reduces by 85KΩ, the conductivity of the target material was enhanced greatly, the reduction overpotential for CO2 decreases from −0.82V to −0.64V, which lead to a large improvement on electrocatalytic activity finally. Thus, the Co-doped MoS2 NPs have both excellent photocatalytic performance and excellent electrocatalytic performance. The main CO2 reduction product is methanol, and the yield of which reaches 35mmolL−1 at 350min. The results have guiding significance for the photoelectric catalyst design, which also have theoretical significance for the photoelectrocatalytic reduction of CO2.

Development of Nanostructured Hybrid Materials for Electrocatalytic and Photoelectrocatalytic Reduction of Carbon Dioxide

There has been growing interest in the electrochemical reduction of carbon dioxide (CO2), a potent greenhouse gas and a contributor to global climate change, and its conversion into useful carbon-based fuels or chemicals. Numerous homogeneous and heterogeneous catalytic systems have been proposed to induce the CO2 reduction and, depending on the reaction conditions various products that include carbon monoxide, oxalate, formate, carboxylic acids, formaldehyde, acetone or methanol, in addition to various hydrocarbons at different ratios. Given the fact that the CO2 molecule is very stable, its electroreduction processes are characterized by large overpotentials. To produce highly efficient and selective electrocatalysts, the transition-metal-based molecular materials are often considered. It is believed that, during electroreduction, the rate limiting step is the protonation of the adsorbed CO product to form the CHO adsorbate. Because reduction of CO2 can effectively occur by hydrogenation, to optimize the conventional electrocatalytic approach, we propose such a model catalytic system as nanostructured metallic palladium capable of absorbing reactive hydrogen in addition to the ability to adsorb monoatomic hydrogen at the interface. Under such conditions, the two-electron reduction of CO2 typically to CO is favored. To produce highly dispersed and reactive nanoparticles, we generate them by electrodeposition from N-coordination complexes of palladium(II). The resulting metallic Pd nanoparticles, rather than Pd cationic species, are stabilized and activated by nitrogen coordination centers from the macromolecular matrix. In the present research, we demonstrate that stabilization and activation of highly dispersed nanostructured metallic Pd centers with a supramolecular architecture of “privileged ligands” results in the electrocatalytic enhancement of the CO2 reduction. Reduction of carbon dioxide begins now at less negative potentials and is accompanied by significant enhancement of the CO2-reduction current densities. Among important issues are specific interactions between nitrogen coordinating centers and metallic palladium sites at the electrocatalytic interface. Another possibility to enhance electroreduction of carbon dioxide is to explore direct transformation of solar energy to chemical energy using transition metal oxide semiconductor materials. We show here that, by intentional and controlled combination of metal oxide semiconductors, we have been able to drive effectively photoelectrochemical reduction of carbon dioxide. The combination of titanium (IV) oxide (TiO2) and copper (I) oxide (Cu2O) has been explored toward the reduction of carbon (IV) oxide (CO2) before and after sunlight illumination. Application of the hybrid system composed of both above-mentioned oxides resulted in high current densities originating from photoelectrochemical reduction of carbon dioxide mostly to methanol (CH3OH), as demonstrated upon identification of final products using conventional and mass-spectrometry assisted gas chromatography. On mechanistic grounds, the role of TiO2 seems to be not only stabilizing: the oxide is also expected to prevent the recombination of charge carriers.

High-Yield and Selective Photoelectrocatalytic Reduction of CO2 to Formate by Metallic Copper Decorated Co3O4 Nanotube Arrays

Carbon dioxide (CO2) reduction to useful chemicals is of great significance to global climate and energy supply. In this study, CO2 has been photoelectrocatalytically reduced to formate at metallic Cu nanoparticles (Cu NPs) decorated Co3O4 nanotube arrays (NTs) with high yield and high selectivity of nearly 100%. Noticeably, up to 6.75 mmol·L(–1)·cm(–2) of formate was produced in an 8 h photoelectrochemical process, representing one of the highest yields among those in the literature. The results of scanning electron microscopy, transmission electron microscopy and photoelectrochemical characterization demonstrated that the enhanced production of formate was attributable to the self-supported Co3O4 NTs/Co structure and the interface band structure of Co3O4 NTs and metallic Cu NPs. Furthermore, a possible two-electron reduction mechanism on the selective PEC CO2 reduction to formate at the Cu–Co3O4 NTs was explored. The first electron reduction intermediate, CO2 ads•–, was adsorbed on Cu in the form of Cu–O. With the carbon atom suspended in solution, CO2 ads•– is readily protonated to form the HCOO– radical. And HCOO– as a product rapidly desorbs from the copper surface with a second electron transfer to the adsorbed species.

Enhanced photoelectrochemical and sensing performance of novel TiO2 arrays to H2O2 detection

Ag-decorated TiO2 nanowire arrays were facilely prepared by H2O2 corrosion of Ti and subsequent photodeposition of Ag. Array structures and photoelectric properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis absorption spectroscopy and electrochemical methods. These results show that Ag quantum dots are evenly distributed on the surface of TiO2 nanowires. With an Ag content of 0.4at%, the electrode's photocurrent density and photoconversion efficiency obtained optimum values of 0.29mA/cm2 and 8.55%, respectively. The enhanced photoelectrochemical properties with Ag modification can be attributed to the extended visible light absorption range and improved separation of photo-generated carriers. Additionally, the modified nanowire arrays exhibited much stronger photoelectrocatalytic reduction activity toward hydrogen peroxide in comparison with pure TiO2 arrays or previously reported Ag electrodes.

A sol–gel derived, copper-doped, titanium dioxide–reduced graphene oxide nanocomposite electrode for the photoelectrocatalytic reduction of CO2to methanol and formic acid

Highly efficient photoelectrocatalytic reduction of CO2into methanol and formic acid at Cu doped RGO–TiO2photoelectrode.

Evaluation of the Parameters Affecting the Photoelectrocatalytic Reduction of CO2 to CH3OH at Cu/Cu2O Electrode

Evaluation of the Parameters Affecting the Photoelectrocatalytic Reduction of CO2 to CH3OH at Cu/Cu2O Electrode

Vertically-aligned sandwich nanowires enhance the photoelectrochemical reduction of hydrogen peroxide: Hierarchical formation on carbon nanotubes of cadmium sulfide quantum dots and Prussian blue nanocoatings

We describe a vertically-aligned array of sandwiched nanowires comprising Prussian blue (PB) nanocoating-carbon nanotube (CNT) core–shell structures with CdS particles positioning at the core/shell interface, viz. PB/CdS/CNT. The PB/CdS/CNT electrode thus constructed are noticeable in synchronically harvesting photon-, ionic-, and chemical-energies, respectively, from visible light radiation, K+ uptaking and releasing, and the reduction of H2O2. In 0.2M K2SO4 aqueous solution, the photoelectrocatalytic reduction of 1.5mM H2O2 at PB/CdS/CNT delivered the current density as high as 1.91mA/cm2 at reduced overpotential, that is, three times that at the Pt/C. This superb performance is causally linked to the judicious choice of materials and their assembly into defining sandwich nanostructures wherein the three components closely cooperate with each other in the photoelectrocatalytic reduction of H2O2, including photo-induced charge separation in CdS, spontaneous electron injection into PB due to its relatively low Fermi level, and the electrocatalytic reduction of H2O2 by PB via an electrochemical–chemical–electrochemical reaction mechanism. The structural alignment of PB/CdS/CNT ensures the simplest pathway for the mass diffusion and electron shuttle, and a high surface area accessible to the chemical and electrochemical reactions, so as to minimize the concentration- and electrochemical-polarization and thus ensure the fast overall kinetics of the electrode reaction.

Application of Coordinatively Supported and Activated Palladium Nanoparticles to Enhance Electrocatalytic Reduction of Carbon Dioxide

There has been growing interest in the electrochemical reduction of carbon dioxide (CO2), a potent greenhouse gas and a contributor to global climate change, and its conversion into useful carbon-based fuels or chemicals. Numerous homogeneous and heterogeneous catalytic systems have been proposed to induce the CO2 reduction and, depending on the reaction conditions (applied potential, choice of buffer, its strength and pH, local CO2 concentration or the catalyst used), various products that include carbon monoxide, oxalate, formate, carboxylic acids, formaldehyde, acetone or methanol, as well as such hydrocarbons as methane, ethane, and ethylene, are typically observed at different ratios. These reaction products are of potential importance to energy technology, food research, medical applications and fabrication of plastic materials. Given the fact that the CO2 molecule is very stable, its electroreduction processes are characterized by large overpotentials, and they are not energy efficient. To produce highly efficient and selective electrocatalysts, the transition-metal-based molecular materials are often considered. Because reduction of CO2 can effectively occur by hydrogenation, in the present work, we concentrate on such a model catalytic system as nanostructured metallic palladium capable of absorbing reactive hydrogen in addition to the ability to adsorb monoatomic hydrogen at the interface. We are going to demonstrate that palladium nanocenters can be generated within the coordination architecture of tridentate Schiff-base-ligands by electrodeposition from the supramolecular complex of palladium(II), [Pd(C14H12N2O3)Cl2]2∙MeOH. The resulting Pd nanoparticles (diameters, 5-10 nm) are stabilized and activated by nitrogen coordination sites, and the electrocatalytic system exhibits appreciable activity toward reduction carbon oxide (IV) in 0.1 mol dm-3 KHCO3. The respective voltammetric peak currents are ca. three times larger than those observed at conventional palladium nanoparticles (diameter, ca. 10-20 nm) under analogous experimental conditions and at the same loading of palladium (100 μg cm-2). Despite that fact that the degree of agglomeration of nanostructured palladium is much lower when it has been generated within the macromolecular network, it is reasonable to expect that some specific interactions between nitrogen coordination centers and metallic Pd exist. The process of electrosorption of hydrogen at the Schiff-base-ligand supported palladium nanostructures seems to be more reversible (when investigated in KHCO3) and dominated by the hydrogen absorption rather than the surface adsorption phenomena (characteristic of conventional Pd nanoparticles). We are also going to address the possibility of combining copper oxide nanostructures together with coordinatively supported Pd nanocenters to drive photoelectrocatalytic reduction of carbon dioxide. Acknowledgement We appreciate collaboration with Adam Gorczynski, Maciej Kubicki, and Violetta Patroniak from Faculty of Chemistry, Adam Mickiewicz University, Poznan, Poland that has led to fabrication of functionalized palladium supramolecular coordination compound.