Catalytic Activity For Oxidation Research Articles

Photothermal Catalytic Removal of 1,2-DCE with High HCl Selectivity over the Brønsted Acid-Enriched Sulfur-Doped MOFs.

Chlorinated volatile organic compounds come from a wide range of sources and are highly toxic, posing a serious threat to biological health and the environment. Herein, a high-efficiency and energy-saving photothermal synergistic catalytic oxidation method was developed for the removal of 1,2-dichloroethane (1,2-DCE). Compared to traditional thermocatalysis, the 1,2-DCE conversion over Ru-U6S in photothermal synergistic catalysis at 340 °C increased by approximately 44% not only reducing energy consumption but also avoiding the instability of MOF structure caused by high reaction temperature. The excellent photothermal catalytic oxidation activity was derived from the synergistic effect of photo- and thermocatalysis. Ru-U6S demonstrated excellent 1,2-DCE adsorption capacity and stronger light utilization and could produce more reactive oxygen species (•OH and •O2-) after light illumination, which participated in the oxidation reaction, promoting the release of the active site of the catalyst. The results of H2O-TPD and NH3-DRIFTS exhibited that the use of S-containing ligands in the synthesis process increased the hydroxyl groups and Brønsted acid sites, significantly improved the selectivity of CO2 and HCl in the oxidation process, and reduced the release of chlorine-containing byproducts. This work provides a high-efficiency and energy-saving strategy for removing chlorinated volatile organic compounds and increasing the selectivity of ideal products directly with MOFs directly.

Generation of oxygen vacancies in CuO/TiO2 heterojunction induced by diatomite for highly efficient UV–Vis-IR driven photothermal catalytic oxidation of HCHO

Photothermal catalytic oxidation is a promising and sustainable method for the degradation of indoor formaldehyde (HCHO). However, the excessively high surface temperature of existing photothermal catalysts during catalysis hinders the effective adsorption and degradation of formaldehyde under static conditions. Catalyst loading and oxygen vacancies (OVs) modulation are commonly employed strategies to reduce the photothermal catalytic temperature and enhance the efficiency of photothermal catalytic oxidation. In this work, a p-n type CuO/TiO2 heterojunction is successfully loaded onto diatomite using a wet precipitation method. Under the irradiation of a 300W xenon lamp, the prepared composite material achieved a 100% removal rate of HCHO within 2 h, with a 98% conversion rate to CO2, surpassing the performance of both individual photocatalysts and thermocatalysts. Additionally, by adjusting conditions such as light irradiation and temperature, we have demonstrated that this material exhibits synergistic photothermal catalytic properties. Based on HRTEM, XPS, Raman, and EPR analyses, the introduction of diatomite as a catalyst support was shown to effectively increase the number of OVs. Experimental results, along with O2-TPD, photoelectrochemical characterization, and radical detection, demonstrate that the presence of OVs enhances the oxidative efficiency of both photocatalysis and thermocatalysis, as well as the UV–Vis-IR photothermal catalytic performance. The ternary composite material generates weak hydroxyl (•OH) and superoxide (•O2−) radical under high-temperature with dark conditions, indicating its catalytic oxidation activity under this condition. The increase in temperature and the expansion of the spectral range both enhance the generation of these radicals. In summary, this work demonstrates that the use of diatomite as a support increases the material's specific surface area and OVs content, thereby enhancing adsorption and photothermal catalysis. It elucidates the enhanced catalytic degradation mechanism of this mineral-based photothermal catalyst.

Microfibrous Carbon Paper Decorated with High-Density Manganese Dioxide Nanorods: An Electrochemical Nonenzymatic Platform of Glucose Sensing

Nanorod structures exhibit a high surface-to-volume ratio, enhancing the accessibility of electrolyte ions to the electrode surface and providing an abundance of active sites for improved electrochemical sensing performance. In this study, tetragonal α-MnO2 with a large K+-embedded tunnel structure, directly grown on microfibrous carbon paper to form densely packed nanorod arrays, is investigated as an electrocatalytic material for non-enzymatic glucose sensing. The MnO2 nanorods electrode demonstrates outstanding catalytic activity for glucose oxidation, showcasing a high sensitivity of 143.82 µA cm−2 mM−1 within the linear range from 0.01 to 15 mM, with a limit of detection (LOD) of 0.282 mM specifically for glucose molecules. Importantly, the MnO2 nanorods electrode exhibits excellent selectivity towards glucose over ascorbic acid and uric acid, which is crucial for accurate glucose detection in complex samples. For comparison, a gold electrode shows a lower sensitivity of 52.48 µA cm−2 mM−1 within a linear range from 1 to 10 mM. These findings underscore the superior performance of the MnO2 nanorods electrode in both sensitivity and selectivity, offering significant potential for advancing electrochemical sensors and bioanalytical techniques for glucose monitoring in physiological and clinical settings.

Insights into the Synergistic Catalytic Effect of TiO2 Supported V-W Oxides for Selective C-H Bond Oxidation of Cyclohexane to KA Oil.

It is urgent to develop an efficient and stable non-noble metal catalyst for selective C-H bond oxidation of cyclohexane. Herein, a series of V-W oxides supported on TiO2catalysts (V-W/TiO2) were fabricated. The V-W/TiO2catalysts exhibited much higher catalytic activity for the selective oxidation of cyclohexane to KA oil, compared to that of V/TiO2and W/TiO2catalysts. The good distribution of active metals and the synergistic effect were responsible for the enhanced catalytic activity. H2-TPR results disclosed that the presence of V inV-W/TiO2 affected the reducibility of W6+species, and XPS verified that an electronic interaction was formed between them. Such results led to good catalytic reusability of V-W/TiO2catalyst during the reactions, and no obvious activity loss was found after six runs. The reaction mechanism was investigated, and the results verified that hydroxyl radicals generated from H2O2homolysis were the main active oxidative species. Theoretical study revealed that V dopant could regulate electronic structure of adjacent O atom, facilitating the adsorption of cyclohexane, and lower energy was needed for the rate-limiting step over V-W/TiO2during the whole oxidation reaction. This work developed an efficient V-W/TiO2catalyst for the selective oxidation of cyclohexane via a synergistic effect.

Studies on a novel oxo-vanadium(V) complex of a tridentate ONO Schiff base ligand: Synthesis, characterization, X-ray crystal structure, Hirshfeld surface analysis, biological and catalytic activity

This study reports the successful synthesis and characterization of a novel oxovanadium(V) complex, [VO(L)(MeOH)(MeO)], prepared from 2-hydroxy-3-methoxybenzaldehyde and 2-methyl-3-aminoquinazoline. To elucidate the structure of the complex, we employed comprehensive characterization techniques such as CHN analysis, molar conductivity measurements, FT-IR, 1H NMR, UV-Vis spectroscopy, and single-crystal X-ray diffraction. The X-ray analysis confirmed an octahedral geometry around the V(V) center, coordinated with donor atoms from the deprotonated Schiff base ligand, an oxido group, a methanol molecule, and a methoxy group. Hirshfeld surface analysis was employed to evaluate intermolecular interactions.Furthermore, the complex exhibited impressively efficient catalytic activity in glucose oxidation under mild conditions (aqueous solution, room temperature, O2 oxidant), achieving a conversion rate of 98 %. Additionally, the antibacterial activity of the ligand and complex against various bacterial strains, including Escherichia coli, Staphylococcus aureus, Pseudomonas aeruginosa, and Bacillus cereus, was evaluated. The results demonstrated promising antibacterial potential of the [VO(L)(MeOH)(MeO)] complex, particularly against E. coli, P. aeruginosa, and B. cereus. These findings suggest potential applications of this new oxovanadium(V) complex in both catalysis and antibacterial treatments.

Plasma-Induced Oxygen Defect Engineering in Perovskite Oxide for Boosting Oxygen Evolution Reaction.

Perovskite oxides are considered highly promising candidates for oxygen evolution reaction (OER) catalysts due to their low cost and adaptable electronic structure. However, modulating the electronic structure of catalysts without altering their nanomorphology is crucial for understanding the structure-property relationship. In this study, a simple plasma bombardment strategy is developed to optimize the catalytic activity of perovskite oxides. Experimental characterization of plasma-treated LaCo0.9Fe0.1O3 (P-LCFO) reveals abundant oxygen vacancies, which expose numerous active sites. Additionally, X-ray photoelectron spectroscopy and X-ray absorption fine structure analyses indicate a low Co valence state in P-LCFO, likely due to the presence of these oxygen vacancies, which contributes to an optimized electronic structure that enhances OER performance. Consequently, P-LCFO exhibits significantly improved OER catalytic activity, with a low overpotential of 294mV at a current density of 10mAcm-2, outperforming commercial RuO2. This work underscores the benefits of plasma engineering for studying structure-property relationships and developing highly active perovskite oxide catalysts for water splitting.

Cobalt and nitrogen co-doped hollow periodic mesoporous organosilica spheres activated by potassium chloride for selective oxidation of ethylbenzene.

Enhancing the exposure of metal active sites and maximizing metal atom utilization are critical challenges in heterogeneous catalysis. To solve these issues, heterogeneous catalysts are usually activated by chemicals. Herein, potassium chloride (KCl) was used as an activator to prepare cobalt-nitrogen co-doped (Co-Nx) hollow periodic mesoporous organosilica spheres (Co-Nx/HPMOs-KCl). Co-Nx/HPMOs-KCl showed outstanding catalytic activity for the selective oxidation of ethylbenzene to acetophenone, with a conversion of up to 94.0% for ethylbenzene and a high selectivity of 98.4% towards acetophenone. Additionally, Co-Nx/HPMOs-KCl maintained excellent catalytic performance for the oxidation of ethylbenzene after six cycles. The excellent performance of Co-Nx/HPMOs-KCl was attributed to the activation of KCl, which increased the specific surface area of the catalyst and thus facilitated the exposure of more metal active sites. After the removal of unstable metal species through further acid treatment, the remaining metal active sites were thus fully exposed and stably embedded in the framework of the hollow periodic mesoporous organosilica spheres (HMPOs). This work presents an efficient catalyst and offers new insights for the improvement of heterogeneous catalysts.

Mn/CeO2 contains enriched surface lewis acid sites and pore structures accelerated catalytic oxidation of propane at low temperature

The development of highly efficient non-precious metal catalysts for the low-temperature catalytic oxidation of volatile organic compounds (VOCs) is a critical imperative in VOCs control. In this study, a series of highly active CeMnOx catalysts with Mn-doped CeO2 were investigated. The catalysts (WHSV=30,000 mL g−1 h−1) exhibited the highest catalytic propane oxidation activity (T90 = 230 °C) and excellent stability over 600 h, When the Mn:Ce ratio was 2.5. The introduction of Mn doping resulted in modifications to the pore structure of CeO2, leading to an increase in specific surface area and enhanced gas transfer kinetics. Additionally, it induced surface electronic defects and elevated the concentration of acidic sites, thereby facilitating the adsorption and activation of propane. Consequently, these improvements contributed to an enhanced catalytic performance of the catalyst. The in-situ DRIFTS infrared spectra revealed that Mn doping reduced the activation energy of the reaction and facilitated the conversion of acetone groups as well as decomposition of carboxylic acid groups.

Super-exchange interaction enables Fe2−xMnxO3 perovskite with excellent catalytic oxidation activity toward hexabromocyclododecane under humidity

Although enhancing the catalytic oxidation activity is a hotspot in thermal-driven catalytic disposal of persistent organic pollutants, few studies have managed to improve catalysts' water-resistance properties. Herein, we developed Fe2−xMnxO3 perovskite to boost the catalytic oxidation of hexabromocyclododecane under humidity by modulating its super-exchange interaction (SEI, Fe3+ + Mn3+ → Fe2+ + Mn4+). Fe0.4Mn1.6O3, with the strongest SEI, exhibits the biggest oxidation rate-constant, which is 3 times higher than that of commonly used Fe2O3 without SEI. Notably, unlike Fe2O3 which deactivates at a relative humidity of 5 %. Fe0.4Mn1.6O3 maintains its activity and is even boosted by 22 % compared to dry conditions. Mechanistic insights reveal that SEI between Fe and Mn enhances the reactivity of Mn4+- linked Olatt by lowering the reductive temperature from Mn4+ to Mn3+. Meanwhile, SEI promotes the adsorption of the associatively adsorbed H2O (HOH-type water) by reducing adsorption energy, thereby facilitating the formation of hydroxyl species, which are crucial for the oxidation process under humidity.

Efficient ammonia conversion in proton conducting fuel cells: Combined application of dendritic anodes and nanofiber catalysts

Ammonia, with its high hydrogen content, serves as an optimal carbon-free medium for indirect hydrogen storage, making it ideal for fuel cells. Nevertheless, the limited anodic catalytic activity of Proton-conducting solid oxide fuel cells (PCFCs) significantly hampers NH3 utilization efficiency and overall performance. This study introduces efficient nano-catalysts deposited onto dendritic anodic microchannels, leading to the formation of an in-situ ammonia decomposition reactor for internal ammonia gas conversion. Compared to conventional cells, this cell, equipped with a catalyst bed, shows a 25% increase in peak power density and a 20%–30% enhancement in NH3 utilization efficiency. Additionally, ammonia undergoes efficient decomposition on anodic metallic nickel, which prevents nickel nitridation and improves cell stability. The augmented stability of these cells is evidenced by their prolonged operational lifespan under constant current conditions, extending from 63 to 108 h, thus marking a substantial enhancement in the system's durability and reliability.

Boosting toluene destruction by engineering surface acidity–alkalinity in defective cobalt oxide catalyst

The surface acidity and alkalinity of catalysts played a decisive role in the destruction of Volatile organic compounds (VOCs). In this study, a series of Co3O4 catalysts were synthesized under different temperatures by calcining metal organic frameworks (MOFs). By controlling the temperature, the organic linkers were effectively eliminated, resulting in catalysts with a high specific surface area due to the preservation of the parent structure of the MOFs. Among the catalysts tested, Co3O4−350 (calcined at 350 °C) demonstrated the highest catalytic activity for toluene oxidation (T90 =231 ℃) and reliable water resistance (3 vol.% water vapor). The efficacy was attributed to the high ratio of reactive oxygen species and high valence Co species, weaken Co−O bond strength as well as high concentration of oxygen vacancies. In situ diffuse reflectance infrared Fourier transform spectroscopy (in situ DRIFTS) demonstrate that acidity–alkalinity is crucial in the adsorption and activation, while oxygen vacancies were found to be essential for deep oxidation.

Revealing the Effect of Anion Regulation in NiCo2X4 (X = O, S, Se, Te) on Photoassisted Methanol Electrocatalytic Oxidation.

Designing nonprecious metal anode catalysts for photoassisted direct methanol fuel cells (PDMFCs) remains a challenge. As a semiconductor catalyst with a spinel structure, NiCo2O4 has good methanol catalytic oxidation activity and photocatalytic activity, making it a highly promising anode non-noble metal catalyst for PDMFCs. However, compared with the noble metal catalyst, the photoelectrocatalytic activity remained to be improved. In this report, an anion regulation strategy was adopted to improve the photoassisted methanol electrocatalytic activity. Using a CoNi-Aspartic (CoNi-Asp) nanorod as the precursor, the anion-regulated NiCo2X4 (X = O, S, Se, Te) was prepared by oxidation, sulfuration, selenization, and telluridation reactions. The regulation of anions and their effects on the electronic structure, intermediate product, and photoelectric catalytic performance of NiCo2X4 (X= O, S, Se, Te) was systematically discussed. Photoelectrochemical characterization and adsorption energy of •OH revealing the volcano-like correlation between the anion in NiCo2X4 (X = O, S, Se, Te) and their photoelectrocatalytic performance. The narrowest band gap (2.239 eV), the highest •OH adsorption energy (-3.32 eV), and the highest ratio of Co3+/Co2+ (2.19) ensure the best photoelectric catalytic performance of NiCo2S4, under the visible light irradiation, the photoresponse current density was 1.9 A g-1, the current density at 0.6 V was up to 21.9 A g-1. After 9 h of stability testing, the current retention rate was 80%. This report sheds an idea for the rational design of non-noble anode catalysts for PDMFCs.

Morphology Variation of Ternary PdCuSn Nanocrystalline Assemblies and Their Electrocatalytic Oxidation of Alcohols.

Metal alloys not only increase the composition and spatial distribution of elements but also provide the opportunity to adjust their physicochemical properties. Recently, multimetallic alloy nanocatalysts have attracted great attention in energy applications and the chemical industry. This work presents the production of three ternary PdCuSn nanocrystalline assemblies with similar compositions via a one-step hydrothermal method. The shape variation of assembly units from nanosheets and nanowires to nanoparticles were realized by adjusting the percentage of Sn in metal precursors. Experimental data show that PdCuSn nanowire networks showed the best catalytic activity by virtue of their optimized morphological characteristics and microscopic electronic structure. With electrooxidation of methanol, ethanol, ethylene glycol, and glycerol at 30 °C, PdCuSn nanowire networks demonstrated catalytic activity of 1129, 2111, 2540, and 1445 mA mg-1, respectively. The catalytic activity for alcohol oxidation is attributed to the production of the electronic structure and morphology features that are most suitable. This is achieved by introducing the proper quantities of Cu and Sn components in the first stage of synthesis. This study would help with the construction of high-efficiency nanostructured alloy catalysts by regulating the electronic structure and morphology.

Theoretical investigation of CO oxidation over polyoxometalate-supported Au cluster catalyst

A polyoxometalate-supported Au cluster catalyst (Au/POM) exhibited high catalytic activity for CO oxidation at room temperature; however, its activity decreased at the reaction temperature above 60 ℃. Density functional theory calculations were performed to elucidate the unique catalytic activities. Our calculations show that the interactions between water molecules accommodated within the defect site of the support and the O2 adsorbed on the Au cluster generate active OOH− species. This OOH− species reacts readily with CO, resulting in high CO oxidation catalytic activity between −40 and 40 degrees Celsius. The activation barrier of CO oxidation over Au/POM in the presence of H2O is much lower than that in the absence of H2O. This is in good agreement with the experimental results, indicating that surface-adsorbed water allows for high CO oxidation catalytic activity around room temperature, whereas the activity decreases at higher temperatures owing to the desorption of surface-adsorbed water molecules.

Bioinspired octanuclear copper cubane complex as an efficient molecular electrocatalyst for water oxidation

Water oxidation catalysts (WOCs) with excellent activity and stability are highly desired. Numerous efforts have been dedicated to develop WOCs mimicking the cubic structure and activity of Mn4CaO5 cluster in oxygen-evolving center (OEC) of photosynthesis system II (PSII). Herein, a octanuclear Cu cluster [Cu8(dpy{OH}O)8(OAc)4]4+ (1, dpy{OH}O− = the monoanion of the hydrated, gem-diol form of di-2-pyridyl ketone) that contains two Cu4O4 cubic fragments with bioinspired structure mimicking the Mn4CaO5 cluster of OEC of natural PSII is developed as efficient homogeneous catalyst for electrochemical water oxidation under near neutral condition for the first time. It exhibits outstanding water oxidation catalytic activity via accelerating oxygen evolution with onset overpotential of 730 mV and appreciable turnover frequency of 20.1 s−1. Collective experiments together confirmed the homogeneity and stability of cluster 1 under long-term water oxidation catalytic cycle. Kinetic study reveals the water nucleophilic attack (WNA) catalytic mechanism occurs on the coordination unsaturated Cu center of the cluster. This work provides the inspiration of the development of robust bioinspired catalyst for electrochemical water oxidation.

Oxygen vacancy–rich K-Mn3O4@CeO2 catalyst for efficient oxidation degradation of formaldehyde at near room temperature

Synthesis of catalysts with high catalytic degradation activity for formaldehyde (HCHO) at room temperature is highly desirable for indoor air quality control. Herein, a novel K-Mn3O4@CeO2 catalyst with excellent catalytic oxidation activity toward HCHO at near room temperature was reported. In particular, the K addition in K-Mn3O4@CeO2 considerably enhanced the oxidation activity, and importantly, 99.3 % conversion of 10 mL of a 40 mg/L HCHO solution at 30 °C for 14 h was achieved, with simultaneous strong cycling stability. Moreover, the addition of K species considerably influenced the chemical valence state of Mn from +4 (ε-MnO2) to +8/3 (Mn3O4) on the surface of CeO2, which obviously changed the tunnel structure and the number of oxygen vacancies. One part of K species is uniformly dispersed on K-Mn3O4@CeO2, and the other part exists in the tunnel structure of Mn3O4@CeO2, which is mainly used to balance the negative charge of the tunnel and prevent collapse of the structure, providing enough active sites for the catalytic oxidation of HCHO. We observed a phase transition from tunneled KMnO2 to Mn3O4 to tunneled MnO2 with the decreasing K+ content, in which K-Mn3O4@CeO2 exhibited higher HCHO oxidation activity. In addition, K-Mn3O4@CeO2 exhibited lower oxygen vacancy formation and HCHO adsorption energies in aqueous solution based on density functional theory calculations. This is because the K species provide more active oxygen species and richer oxygen vacancies on the surface of K-Mn3O4@CeO2, promote the mobility of lattice oxygen and the room-temperature reduction properties of oxygen species, and enhance the ability of the catalyst to replenish the consumed oxygen species. Finally, a possible HCHO catalytic oxidation pathway on the surface of K-Mn3O4@CeO2 catalyst is proposed.

Correlating crystallinity regulation in spinel oxides and catalytic activity in electrocatalytic water oxidation

Recently, the electro-Fenton (EF) process by coupling cathodic two-electron oxygen reduction reaction (2e- ORR) with anodic oxygen evolution reaction (OER) has emerged as a potentially viable technology, while the sluggish OER is the main bottleneck. As promising OER catalysts, the amorphous and crystal phases of spinel oxides display high activities and electrical conductivity, respectively. Efforts to produce amorphous/crystal spinel oxides have progressed slowly, and how an amorphous/crystal structure benefits the catalytic performances remains elusive. Herein, Fe-doped NiCo2O4 (Fe-NiCo2O4) was used as a model catalyst to explore the effect mechanism of crystallinity controlled by annealing temperature on OER performance. The results display that the Fe-NiCo2O4 obtained at 300 ℃ shows amorphous/crystal structure, which facilitates the active site exposure and the charge transfer, leading to superior OER activity and catalytic stability. Based on the crystallinity regulation of OER catalysts, we propose an anodic optimized strategy to upgrade the EF-related processes by effectively providing O2 produced in the anode.

Influence of iron doping in mesoporous ceria on the physicochemical properties and catalytic activity in styrene oxidation

A series of nanosized Fe-Ce binary oxides (2, 5, 10, 20, and 30 wt% Fe) and pure oxides of Fe and Ce were prepared by the template-assisted coprecipitation method and evaluated for styrene oxidation. The synthesised binary oxides were investigated by Powder X-ray diffraction(PXRD), N2-physisorption, X-ray fluorescence (XRF), Field emission scanning electron microscopy (FE-SEM), Highresolutiontransmission electron microscopy (HR-TEM), Raman spectroscopy, Fourier transform infrared spectroscopy (FT-IR), Ultraviolet–Visiblediffuse reflectance spectroscopy (UV–Vis DRS), X-ray photoelectron spectroscopies (XPS), and Hydrogen-temperature programmed reduction (H2-TPR). In particular, the influence of quantity of doped iron on the structure, phase composition, surface morphology, reducibility, and the catalytic performance of ceria is deeply investigated. All the synthesized Fe-doped ceria catalysts exhibited the formation of solid solutions, but a little α-Fe2O3 segregated on the surface of ceria at 20 and 30 wt% Fe doped ceria. Among all Fe-Ce binary oxides, the 10 wt% Fe-doped ceria catalyst demonstrated superior efficiency due to its optimal Fe content which achieved the high surface area, lattice oxygens, reducibility, and low crystallinity, as confirmed by BET (Brunauer-Emmett-Teller) measurements, XPS, H2-TPR and powder XRD analysis, respectively. To optimize the reaction conditions, effect of several experimental variables, such as reaction temperature, duration, catalyst quantity, styrene/tert-Butyl hydroperoxide (TBHP) mole ratio, and solvent polarity were investigated. Furthermore, the catalyst stability and consistent activity were confirmed by testing six reusability cycles.

Improvements in Long-Term Durability of CO2 Electrolyzer Producing Formate Designed for Integration with Solar Cells for Artificial Photosynthesis

Artificial photosynthetic cells have been extensively studied for carbon neutrality, yet in lab-scale. We have previously constructed practically large-sized cells consisting of CO2 electrolyzers and crystalline silicon solar cells.1,2 Our CO2 electrolyzers adopt a facing cathode-anode configuration, using a Ru complex polymer (RuCP) catalyst realizing a low overpotential for CO2 reduction and an IrO x -based catalyst with a high catalytic activity for water oxidation.3 1000 cm2-sized cells achieved a solar-to-chemical energy-conversion efficiency (η STC) of 7.2%,1 and a further scaled-up 1 m2-cell demonstrated a higher η STC of 10.5%, yielding a large formate production rate of 1.2 mol/h.2 In the present study, we improved the long-term durability of the CO2 electrolyzer. We prepared the 75 cm2-sized CO2 electrolyzer using the improved cathode and the anode, and achieved high formate Faradaic efficiencies (FE) exceeding 80% and electricity-to-chemical energy-conversion efficiencies (η ETC) of around 60% even after 3000 h operation under practical conditions, as shown in Fig. 1.In the previous large-sized cells, the operating current gradually decreased during continuous operation within dozen of hours. We investigated the causes of the degradation and identified three key factors. Two of these factors were associated with the cathode electrodes: detachment of the RuCP catalyst from the carbon supports and peeling off of the carbon supports from the conducting Ti substrates. An introduction of a pyrrole derivative containing amino group in the RuCP, coupled with an application of a UV-ozone treatment to create carboxyl groups on the carbon supports, effectively reduced the detachment of the RuCP catalyst by forming strong chemical bonds. A newly-developed chemically-resistant graphite adhesive composed of graphite particles and a polyvinylidene fluoride (PVDF) binder prevented the carbon supports from peeling off from the Ti-plates. The post-loading process of the RuCP, i.e., RuCP-loading on the carbon supports already-bonded on the Ti-plates using the new adhesive eliminated the detrimental impact of the heat treatment for curing the adhesive. The third factor involved detachment of the anode catalyst of IrO x particles from the Ti-plates.4 Therefore, we replaced the IrO x anodes with highly durable counterparts comprising IrO x -TaO x /Pt-Metal oxide/Ti-plates.Another critical issue we addressed was the validity of laboratory-based evaluations for reflecting outdoor operations. In our previous study, we vertically installed the integrated CO2 electrolyzers and solar cells on the ground and evaluated their performance under continuous simulated sunlight (ca. 1 sun).2,3 This vertical setup was chosen to prevent a decrease in η STC caused by crossover reactions that would occur when the electrolyzers are inclined. Indeed, it has been reported that oxygen reduction reaction (ORR) of the O2 bubbles generated at the anode and transferred to the cathode can be substantial in a single-chamber water-splitting reactor.5 By contrast, although the present CO2 electrolyzer was installed at an inclined angle of 30 °, which is approximately the optimal value for receiving more solar energy, the crossover reactions were well-suppressed because the porous separator film inserted between the facing cathode and anode impeded the transfer of O2 bubbles from the anode to the cathode. However, the use of a separator film raised another issue: the O2 bubbles trapped on the film narrowed the effective film area. Intermittent operation corresponding to changes in solar energy during the day mitigates the detrimental impact of the second issue.Thus, we established the groundwork for the widespread use of integrated CO2 electrolyzers and solar cells for artificial photosynthesis, demonstrating high durability, exceptional FE, and η ETC.References N. Kato, et al., A large-Sized Cell for Solar-Driven CO2 Conversion with a Solar-to-Formate Conversion Efficiency of 7.2%, Joule, (2021) 5, 687.N. Kato, et al., Solar Fuel Production from CO2 using 1 m-square-sized Reactor with a Solar-to-Formate Conversion Efficiency of 10.5%, ACS Sustain. Chem. Eng.,(2021) 9, 16031.T. Arai, S. Sato, T. Morikawa, A Monolithic Device for CO2 Photoreduction to Generate Liquid Organic Substances in a Single-Compartment Reactor, Energy Environ. Sci., (2015) 8, 1998.M. Shiozawa, et al., Improved Durability of Highly Active IrO x Electrodes for Electrocatalytic Oxygen Evolution Reaction, Electrocatalysis, (2022) 13, 830.K. Obata, et al., Multiphase Fluid Dynamics Simulations of Product Crossover in Solar-driven, Membrane-less Water Splitting, Cell Rep. Phys. Sci, (2021) 2, 100358. Figure 1

Optimization of Pd–Co–M (M= Cu, Au, Ni) Catalysts for the Oxidation of Formic Acid Using Scanning Electrochemical Microscopy

Formic acid, a versatile substance with applications as both a fuel and hydrogen storage material, emerges as a promising energy source. When utilized as a hydrogen storage material, a single liter of formic acid yields an impressive 590 liters of hydrogen gas under ambient conditions. Furthermore, as a fuel, the Direct Formic Acid Fuel Cell (DFAFC) stands out as a potential energy solution due to its elevated open-circuit voltage, low toxicity, and reduced permeability of high molecular weight membranes. Efficient catalysts play a pivotal role in enhancing the formic acid oxidation reaction, thereby diminishing the anode overpotential and amplifying the hydrogen production efficiency of DFAFC. The conventional method of manually testing each catalyst for optimal formic acid oxidation performance is both time-consuming and resource-intensive. Consequently, this study employs a substrate collection method based on a scanning electrochemical microscope (SECM) microelectrode for catalyst screening. A ternary catalyst array, primarily comprising PdCo with supplementary elements (Au, Cu, Ni), was crafted using the innovative concept of compositional assembly. The SECM facilitated the determination of the catalyst's surface morphology, energy-dispersive spectroscopy gauged the catalyst composition, and X-ray diffraction, along with X-ray photoelectron spectroscopy, confirmed the crystalline structure composition. To delve into the kinetic aspects of the catalyst for formic acid oxidation, a comprehensive analysis was carried out using cyclic voltammetry, stripping voltammetry, electrochemical impedance spectroscopy, and Tafel slope analysis. The outcomes unveiled that the optimal proportions for the ternary catalysts were Pd2Co6Au2, Pd2Co6Cu2, and Pd2Co6Ni2, with Pd2Co6Au2 exhibiting superior attributes such as lower overpotential, heightened resistance to CO poisoning, and enhanced catalytic activity for formic acid oxidation.