Surface Oxygen Vacancy Concentration Research Articles

Tuning CO2 Hydrogenation to Light Olefin Selectivity via Cu/Zn/Zr Supported on Modified SAPO‐34

AbstractTo alleviate CO2 emissions and reduce reliance on fossil fuels, a groundbreaking bifunctional catalyst system was introduced, which ingeniously merged CZZ with modified SAPO‐34 zeolite, to convert CO2 into light olefins. Different metals were impregnated into SAPO‐34 to form MeSAPO‐34 (Me = Zn, Zr, Mn) and the metal Zr content was altered. Furthermore, CZZ and MeSAPO‐34 was combined into CZZ/MeSAPO‐34 composite catalysts, which was used for CO2 hydrogenation. The MeSAPO‐34 and xZrSAPO‐34 catalysts were rigorously characterized by various techniques, revealing key physicochemical attributes. This innovative approach harnessed the synergistic effects between the metallic CZZ component and the modified zeolite to facilitate a series of reactions, effectively generating C2‐C4‐rich hydrocarbons. Benefiting from weak acid, higher oxygen vacancy concentration and interactions between components, the CZZ/ZrSAPO‐34 catalyst system has shown remarkable efficiency in enhancing the light olefin selectivity. The key aspects of this system are its ability to modulate surface acidity and oxygen vacancy concentration, thus creating favorable conditions for light olefin production via enhanced tandem reaction based on CO2 hydrogenation. This work enriches our insight into designing novel composite catalysts for promoting CO2 conversion and hence mitigating CO2 emissions.

Enhanced photocatalytic CO2 reduction to CH4 on oxygen vacancy-rich NiCo2O4 with surface pits: Synthesis, DFT calculations, and mechanistic insights

Unraveling the influence of surface microstructure in materials on their interaction with CO2 remains a critical challenge in achieving efficient and selective CO2 reduction. In this study, we report the engineering of pit structures on the NiCo2O4 surface for efficient photocatalytic reduction of CO2. Characterization results show that calcination temperature affects the distribution of surface pits and oxygen vacancy concentration. Oxygen vacancy sites accompanying surface pits facilitate the generation and movement of photogenerated electrons and holes, preventing their recombination and promoting the conversion of CO2. The CH4 yield from photocatalytic CO2 reduction reaches 52.4 μmol g−1 with the optimal pitted NiCo2O4 catalyst (PNCO2), significantly surpassing the 18.4 μmol g−1 yield of non-pitted NiCo2O4 (NPNCO). Additionally, PNCO2 improves selectivity from 81.8 % for NPNCO to 94.1 %. Density functional theory calculations show that CO2 adsorption on the PNCO2 surface is significantly enhanced as the d-band center shifts toward the Fermi level. The adsorbed CO2 combines with electrons enriched at the Ni sites at the edges of the surface pits, leading to further activation. The reduction of CO2 to intermediate products such as CHO* is analyzed based on in situ diffuse reflectance infrared Fourier transform spectroscopy, and a possible reaction pathway is proposed. This work offers fresh insights into engineering surface pit structures for the design and synthesis of catalysts for photocatalytic CO2 reduction.

Non-thermal plasma-catalytic ammonia synthesis over alumina-supported iron catalyst: Insights into the effect of alumina calcination temperature

Non-thermal plasma-catalytic ammonia synthesis (NTPCAS) has been regarded as a promising route to store hydrogen by utilizing renewable electricity. Alumina is a suitable support of the catalysts in NTPCAS and its properties can influence the performance of catalysts remarkably. In this study, the influence of the alumina calcination temperatures (Tc) on the catalytic performance of Fe-Al-x (x represents the value of Tc) was analyzed in a dielectric barrier discharge (DBD) reactor for NTPCAS. The results suggested that an increase in Tc transforms the alumina crystalline from γ phase to α phase. The best performance with a synthesized ammonia concentration of 11833 ppm was achieved over Fe-Al-900 with coexisting γ and θ phases of alumina under N2: H2 = 1:1 and SEI = 37.05 kJ/L conditions, which was 37 % higher than that of Fe-Al-800 with only γ phase. In addition, the larger Tc (i.e. 1100 and 1200 °C) decreased the specific surface area, increased the mean catalyst particle size, and led to the non-uniform dispersion of Fe species. The NH3-TPD and XPS studies suggested that an increase in Tc could influence the surface acidity and oxygen vacancy concentration of Fe catalysts, which were crucial to adjusting the catalytic activity for NTPCAS. This study clarifies the value of a suitable design of support of catalysts for improving NTPCAS.

Surface Chemistry Modulation of BaGd0.8La0.2Co2O6-δ As Active Air Electrode for Solid Oxide Cells.

Modulation of the surface chemistry of air electrodes makes it possible to significantly improve the electrocatalytic performance of solid oxide cells (SOCs). Here, the surface chemistry of BaGd0.8La0.2Co2O6-δ (BGLC) double perovskite is modulated by treatment in an acidic citric acid solution. The treatment leads to corrosion on the surface of BGLC particles, and the effect is dependent on the acidity of the solution. As the acidity of solution is low, Ba cations are selectively dissolved out of the BGLC surface, while as the acidity increases, the corrosion becomes more homogeneous. The Ba surface deficiency remarkably increases the concentration of surface oxygen vacancies and electrocatalytic activity of BGLC. To avoid the loss of Ba-deficient surface during the conventional high temperature sintering process, a sintering-free fabrication route is utilized to directly assemble the Ba-deficient BGLC powder into an air electrode. A single cell with the surface Ba-deficient BGLC electrode shows a peak power density of 1.04 W cm-2 at 750 °C and an electrolysis current density of 1.48 A cm-2 at 1.3 V, much greater than 0.64 W cm-2 and 1.02 A cm-2 of the cell with the pristine BGLC, respectively. This work provides a simple and effective surface chemistry modulation strategy for the development of an efficient air electrode for SOCs.

Surface oxygen defect engineering to enhance La0.5Sr0.5Fe0.9Mo0.1O3-δ electrochemical performance for reversible symmetric solid oxide cells

Perovskite oxide-based materials are promising electrode materials for reversible symmetric solid oxide cells (RSSOCs) as they exhibit good catalytic activity and stability in oxidizing and reducing atmospheres. In this study, A-site deficient (La0.5Sr0.5)0.95Fe0.9Mo0.1O3-δ (95LSFMo) is synthesized as an electrode material for RSSOCs. The A-site defect in La0.5Sr0.5Fe0.9Mo0.1O3-δ increases the surface oxygen vacancy concentration, promoting the transport of oxygen ions and enhancing the catalytic activities of oxygen reduction (ORR) and hydrogen oxidization reaction (HOR). 95LSFMo|LSGM|95LSFMo symmetric cell achieves a maximum power density (MPD) of 1.14 W cm−2 at 850 °C. Furthermore, the adsorption and reduction of H2O is also improved. In 50 %H2O-H2, 95LSFMo cell shows a current density of −1.71 A cm−2 at 850 °C and 1.3 V in electrolysis mode and a peak power density of 0.82 W cm−2 in fuel cell mode. The corresponding hydrogen production rate reaches 714.78 ml cm-2h−1. Moreover, the 95LSFMo cell exhibits good reversibility as well as SOEC stability.

Enhancing the Performance of 2D Ni-Fe Layered Double Hydroxides by Cabbage-Inspired Carbon Conjunction for Oxygen Evolution Reactions.

Layered double hydroxide (LDH) nanosheets as one type of two-dimensional materials have garnered increasing attention in the field of oxygen evolution reaction (OER) in recent decades. To address the challenges associated with poor conductivity and limited electron and charge transfer capability in LDH materials, we have developed a straightforward one-pot synthesis method to successfully fabricate a composite material with a microstructure resembling cabbage, which encompasses NiFe-LDH and nanocarbon (referred as NiFe-LDH@C). Atomic force microscopy (AFM) and high-resolution transmission electron microscopy (HRTEM) revealed that the monolayer NiFe-LDH with a height of ~0.5-0.8 nm is uniformly distributed and closely bonded to the carbon support, leading to a significant enhancement in conductivity and facilitating faster electron and charge transfer. Moreover, the NiFe-LDH@C exhibits a substantial number of surface defect sites, which enhances the interaction with oxygen species. This dual enhancement in charge transfer and oxygen species-mediated transfer greatly improves the catalytic OER performance, which is further corroborated by theoretical calculations. Notably, the Ni10Fe6-LDH@C with the highest concentration of surface oxygen vacancies demonstrated superior water oxidation performance, surpassing commercially available RuO2 catalysts; an OER overpotential of 231 mV@10 mA cm-2 with a Tafel slope of 71 mV dec-1 was achieved.

Boosting photocatalytic performance in Cu doped ZnO nanocomposites: Investigation of exciton-free carrier conversion and oxygen vacancy dynamics

The production of photocatalytic materials with strong light absorption ability and high quantum efficiency by simple means is a long-term goal of photocatalytic technology. In this work, we have synthesized Cu doped ZnO nanoparticles by a facile sol-gel method. By introducing Cu impurities, it is shown that the excitons in ZnO have been efficiently separated into free carriers, leading to optimized photocatalytic performance. The surface amorphous layers of the nanoparticles grew thicker at the introduction of Cu atoms into ZnO lattice, which boosted the photocatalytic ability due to the increase of surface oxygen vacancy concentration. This finding provides a direct evidence of quasi-particle-free carrier conversion in Cu doped ZnO, as well as a guidance for fabricating high efficiency ZnO based nano-photocatalysts.

Regulating concentration of surface oxygen vacancies in Bi2MoO6/Bi-MOF for boosting photocatalytic ammonia synthesis

Surface oxygen vacancies (OVs) engineering has been widely adopted as an effective strategy to enhance photocatalytic performance. At present, photocatalytic systems capable of precisely regulating surface OVs concentrations, which could help illuminate the effects of the surface OVs concentration on N2 fixation activity, are still scarce. Herein, bismuth-based metal organic framework (Bi-MOF) was loaded onto the surface of Bi2MoO6 (BMO) as an operable platform, and the OVs concentration in the Bi-MOF component of BMO/Bi-MOF could be regulated by reduction of bismuth ions therein. Experimental results confirm that optimum construction of OVs in the Bi-MOF promotes the photoelectrons transfer from BMO to Bi-MOF, facilitating the activation of N2 at OVs. Consequently, the optimized catalyst shows superior performance in NH3 production, which reaches 125.78 μmol h−1 g−1, 21.4 higher than that of BMO. This work underline the significance of regulating surface OVs concentration, providing inspiration for the development of efficient OVs-modified photocatalysts.

Photocatalytic N-formylation of amines with CO2 over Pt-Bi bimetallic decorated CeO2−x

N-formylation of amines with CO2 is a promising approach to high-efficient utilization of CO2 as C1 feedstock, while conventional thermocatalytic processes suffer from harsh reaction condition and intense energy consumption. In this work, photocatalytic N-formylation of amines with CO2 is achieved at room temperature over Pt-Bi/CeO2−x composite catalyst. The Pt-Bi bimetallic sites increase the concentration of surface oxygen vacancies. Furthermore, the synergistic effects of Pt and Bi improve the light absorption capacity, reduce the band gap energy of the photocatalyst and promote the separation of photoinduced charge carriers. Using PhSiH3 as the reducing agent, the conversion of N-methylaniline reaches 100 % after 3 h irradiation in N, N-dimethylformamide solvent with a N-methylformanilide selectivity of 90.8 %. The composite photocatalyst shows promising cycling stability and universality.

Interfacial carbon quantum dot thin film impacts on morphological and chemical structures of fluorine-doped tin oxide films

Morphology and chemical bonding states, including surface roughness, film density, F-doping, and oxygen vacancy (VO) concentration directly affect the electrical and optical properties of fluorine-doped tin oxide (FTO) films. In this study, morphology and chemical bonding states of FTO films are engineered simultaneously by introducing a carbon quantum dot (CQD) thin film as an interface layer during ultrasonic spray pyrolysis deposition. The abundant oxygen-containing surface functional groups and large surface free energy of the CQD thin film promoted (200) oriented crystal growth and accelerated nucleation of FTO, resulting in smooth and dense FTO film morphology. The abundant carboxyl surface functional groups on the CQDs generate active F− species that are effectively doped into SnO2. Formic acid, formed by dissociation of the carboxyl group, can serve as a strong reducing agent for extracting oxygen atoms from the SnO2 lattice, thereby increasing the VO concentration. The accelerated F-doping and VO concentration result in the generation of additional free electrons. The effects of the optimized CQD on the morphological and chemical structures of FTO films are demonstrated by their superior electrical (sheet resistance of ∼5.7 Ω/□) and optical properties (visible transmittance of ∼85.9 %) compared with bare FTO. Moreover, CQD/FTO used as transparent conducting electrodes in electrochromic (EC) application exhibited improved EC performances, including fast switching speeds (5.3 s and 2.3 s for bleaching and coloration, respectively) and high coloration efficiency (81.1 cm2/C) compared to that of bare FTO.

Photoexcitation assisted oxygen vacancy for enhancing nitrogen fixation with Fe-CeO2

Photoexcitation assisted oxygen vacancy for enhancing N2 fixation was investigated with Fe-CeO2 as photocatalysts. Fe substituted doping of CeO2 promoted the formation of oxygen vacancies (Vo). 5 % Fe-CeO2 exhibited the highest Vo concentration with photocatalytic nitrogen fixation efficiency of 176 μmol·g−1·h−1. The oxygen vacancy could induce the formation of the oxygen vacancy level, which could reduce the band gap energy, attract electrons, and hinder the electron hole recombination. More importantly, the oxygen vacancy level could be used as a springboard to reduce the energy required for N2 activation. In addition, calcination and acid-wash were used to regulate the concentration of surface oxygen vacancies (Vo-s) and bulk oxygen vacancies (Vo-b), respectively. The results showed that acid-wash only reduced the Vo-s concentration, while calcination reduced both the Vo-s and the Vo-b concentration, and the high concentration of Vo and Vo-s was beneficial for photocatalytic nitrogen fixation. The regulation strategy of Vo had guiding significance for improving the photocatalytic performance of metal oxide photocatalysts.

β-Ga2O3 Schottky barrier height improvement using Ar/O2 plasma and HF surface treatments

In this report, we show that Ar/O2 plasma exposure followed by HF treatment improves the Schottky barrier height (SBH) in β-Ga2O3 Schottky barrier diodes (SBDs) by nearly 0.3 eV, resulting in a breakdown voltage (VBR) gain of over 100 V on 2 × 1016 cm−3 doped substrates, without compromising the specific on-resistance. The SBH and VBR enhancement is observed on (2¯01) as well as (001) surfaces. Through extensive surface characterization, the Ar/O2 plasma exposure is shown to amorphize and increase surface oxygen vacancy concentration. HF treatment cleans the surface damage and passivates the surface through fluorine adsorption, leading to Fermi-level de-pinning and SBH improvement. Remarkably, however, the Ar/O2 plasma exposure enhances fluorine adsorption when compared to fluorine treatment alone, resulting in a more substantial improvement in SBH and VBR. Surface clean/treatment plays a critical and fundamental role in determining the quality of the metal/β-Ga2O3 interface. The improved surface treatment process demonstrated in this work can be easily integrated with various field termination methods that can help further improve the β-Ga2O3 SBD performance.

Study on the Catalytic Oxidation of Toluene Using CeO2@S-AZMB Prepared from Spent Zn-Mn Batteries

The recycling and utilization of waste alkaline zinc manganese batteries (S-AZMB) has always been a focus of attention in the fields of environment and energy. However, current research mostly focuses on the recycling of purified materials, while neglecting the direct reuse of waste batteries. Here, we propose a new concept of preparing thermal catalysts by combining unpurified S-AZMB with CeO2 by means of ball milling. A series of characterizations and experiments have confirmed that the combination with S-AZMB not only enhances the thermal catalytic activity of CeO2 but also significantly enhances the concentration of surface oxygen vacancies. In the toluene removal experiment, the temperature (T90) at 90% toluene conversions of CeO2@S-AZMB was 180 °C, lower than the 220 °C for CeO2. More noteworthy is that this S-AZMB-based thermal catalyst can maintain a good structure and thermal catalytic stability in cyclic catalysis.

Phyllantus acidus mediated combustion method synthesised yttria stabilized zirconia, its application as photocatalyst and antibacterial agent

The ceramic material combines different functionalities such as good thermal stability, selective bulk oxygen mobility and high surface oxygen vacancy concentration are the most attracted research to opt for the 8 yttria stabilized zirconia nanomaterial. Nanocomposite 8 yttria stabilized zirconia powder (8YSZ) by bio-mediated combustion synthesis utilizing Phyllanthus acidus fuel. Cubic 8YSZ powder were discovered to be photocatalytic for the deterioration of anionic dyes. The synthesised NP's structural characteristics were assessed with the use of PXRD, UV-Vis, SEM, FTIR and TGA and DTA analyses. Additionally, by monitoring the AO7 coloring change in absorbance under the UV spectroscopy, the photo catalytic action of the 8YSZ on NPs dye has been shown. By tracking the drop in dye concentration relative to the initial dye concentration, the photodegradation of the AO7 organic dye was determined. Investigations have also been conducted on the impacts of operating parameters like pH, catalyst dosage. The present work stated that 8YSZ NP’s have a greater capability for deterioration when exposed to Visible radiation and investigated the antibacterial properties of high-quality ceramic material 8YSZ for use in dentistry.

Dual mechanisms in hydrogen reduction of copper oxide: surface reaction and subsurface oxygen atom transfer.

The study of the reduction of copper oxide (CuO) by hydrogen (H2) is helpful in elucidating the reduction mechanism of oxygen carriers. In this study, the reduction mechanism of CuO by H2 and the process of oxygen atom transfer were investigated through the density functional theory (DFT) method and thermodynamic calculation. DFT calculation results showed that during the reaction between H2 and the surface of CuO, Cu underwent a Cu2+ → Cu1+ → Cu0 transformation, the Cu-O bond (-IpCOHP = 2.41) of the Cu2O phase was more stable than that (-IpCOHP = 1.94) of the CuO phase, and the reduction of Cu2O by H2 was more difficult than the reduction of CuO. As the surface oxygen vacancy concentration increased, it was more likely that the subsurface O atoms transfer to the surface at zero H2 coverage (no H2 molecule on the surface), allowing the surface to maintain a stable Cu2O phase. However, when the H2 coverage was 0.25 monolayer (ML) (one H2 molecule every four surface Cu atoms), the presence of H atoms on the surface made the upward transfer of O atoms from the subsurface more difficult. The rate of consuming surface O atoms in the reduction reaction was greater than the rate of subsurface O atom transfer induced by the reduction reaction and the surface Cu2O phase could not be maintained stably. Through thermodynamic analysis, at high H2 concentration, the reaction between H2 and CuO was more likely to generate Cu, while at low H2 concentration, it was more likely to generate Cu2O. In summary, the valence state of Cu in the reaction process between CuO and H2 depended on the concentration of H2.

Microstructural, electrical and thermal characterization of Dy3+, Sm3+, Er3+, Y3+ and Gd3+ multi-doped cerium dioxide as SOFCs solid electrolytes

The production of electrolytes with high ionic conductivity has been a key challenge in the progressive development of solid oxide fuel cells (SOFCs) for practical applications. Conventional approaches use ionic doping to develop electrolyte materials, such as yttria-stabilized zirconia (YSZ), but challenges remain. The doping systems discovered so far can confirm that co-doping/triple doping can introduce more oxygen vacancies to improve the electrical properties of ceria-based electrolytes compared to unitary doping. Therefore, In this work, we select the optimal dopant based on the criterion of optimal doping in cerium dioxide (effective average ionic radius close to 1.093 Å). And propose a novel multi-doped cerium-based Ce1−x(Dy1/5Sm1/5Er1/5Y1/5Gd1/5)xO2-δ (x = 0.10, 0.15, 0.20, 0.25, 0.30, abbreviated as DSEYG1, DSEYG2, DSEYG3, DSEYG4, DSEYG5) electrolytes to study its microstructure, electrical properties and thermal properties. Dy3+, Sm3+, Er3+, Y3+, and Gd3+ multi-doped electrolyte materials. Over 95% of the relative density values were obtained by sintering DSEYG series samples at 1400 °C. The single-phase cubic fluorite structure, high-density surface microstructure, elemental confirmation, and oxygen vacancy concentration were confirmed using X-ray diffraction, scanning electron microscope, energy dispersive spectrum, transmission electron microscopy, and X-ray photoelectron spectroscopy. Electrical analysis by impedance spectroscopy confirmed the highest value of total ionic conductivity (σ800 °C= 4.04 ×10−2 S/cm) and the lowest value of activation energy (Ea= 0.834 eV) for the DSEYG3 composition. Thermal expansion analysis confirmed the moderate thermal expansion coefficient values for all compositions (TEC =11.12 ×10−6 K−1) in the range of RT-800 °C) and was found to be in good agreement with recently developed materials. The enhanced total ionic conductivity and moderate thermal expansion coefficient of DSEYG3 make it a potential electrolyte material for medium-temperature fuel cells.

Effect of annealing temperature on the formation of oxygen vacancies on the surface of flower-like SnSe/SnO2 heterostructure and visible light catalytic performance

The morphology, structure, and oxygen vacancies in principle determine the light absorption, charge transfer, and separation of photocatalysts, thereby determining their photocatalytic performance. In this study, flower-like SnSe obtained from hydrothermal reactions was oxidized to obtain heterojunctions with SnSe/SnO2. Flower-like SnSe/SnO2 heterojunctions with different concentrations of oxygen vacancies were prepared by annealing them in an argon atmosphere at different temperatures. The flower-like SnSe/SnO2 series with different oxygen vacancies were systematically characterized by TEM, XRD, XPS, PL, and EPR. The research results demonstrate the presence of oxygen vacancies in the flower-like SnSe/SnO2. As the annealing temperature increases, the surface oxygen vacancy concentration shows a trend of first increasing and then decreasing. When the annealing temperature reaches 600 °C, the oxygen vacancy concentration of flower-like SnSe/SnO2 is the highest. Meanwhile, research has shown that surface oxygen vacancies help expand the light absorption range, and the increased valence bandwidth leads to effective charge transfer and separation, thereby promoting visible light photoactivity. SnSe/SnO2-600 °C exhibited excellent visible light photocatalytic activity. The photodegradation of methylene blue (MB) at ≥ 400 nm can reach ∼70% within 120 min. This study verified the route for the introduction of oxygen vacancies via facile calcination and constructed SnSe/SnO2 with surface oxygen vacancies, providing a reference with deep insights for improving photocatalytic activity.

Effectively boosting hydration capacity and oxygen reduction activity of cobalt-free perovskite cathode by K+ doping strategy for protonic ceramic fuel cells

Development of triple-conducting cathode can extend the electrochemically active region to the entire cathode to more effectively promoting oxygen reduction reaction (ORR). Herein, a cobalt-free perovskite Sr1.75K0.25Fe1.5Mo0.5O6−δ (SKFM) was developed as a single-phase triple-conducting cathode material for protonic ceramic fuel cells (PCFCs). Introduction of K into Sr-site leads to a 21.54 % increase in the hydration capacity compared to the undoped Sr2Fe1.5Mo0.5O6−δ (SFM). The bulk diffusion coefficient and surface exchange coefficient of SKFM are 3.8 and 5.2 times higher than those of SFM at 550 °C, respectively. XAS and EPR results demonstrate that the average valence state of Fe and the concentration of surface oxygen vacancies in SKFM are higher than those in SFM. The polarization resistances (Rp) value of SKFM cathode in wet air is 0.06 Ω cm2 at 700 °C, while it is 0.11 Ω cm2 for SFM cathode, which is reduced by 45.5 %, indicating significantly improved ORR activity. The Rp is dominated by the adsorption and diffusion process of oxygen associated with low-frequency part in wet air. The single cell with a configuration of Ni-BZCY4/21-μm-thick BZCY4/SKFM delivers a power output of 1000.8 mW cm−2 in wet H2 at 700 °C and steady operation at 600 °C for a total of 100 h.

Coke formation pathway under various reaction conditions during the production of syngas in a dielectric barrier discharge plasma environment using CeO2 nanorods supported Ni catalysts

Plasma-assisted dry reforming of methane (DRM) was investigated using CeO2 nanorods (NR) supported Ni catalysts in a fixed-bed coaxial dielectric barrier discharge (DBD) reactor. This study individually examined the catalyst support, packing material, and 10 wt% Ni-CeO2 NR catalyst under pure thermal and plasma-assisted thermal DRM environments to explore the plasma-thermal synergy. Support and packing material displayed no discernible reactivity under thermal DRM within 450 °C; however, the catalyst exhibited reactivity beginning around 350 °C. Alternatively, plasma-assisted DRM experiments revealed a distinct reaction occurrence at significantly lower temperatures across all sample types. Introducing plasma demonstrated a significant enhancement in CH4 conversion compared to CO2 conversion. The 10 wt% Ni-CeO2 NR catalyst in plasma-assisted DRM testing showed increasing conversions of CH4 and CO2 with rising temperatures, peaking at 52.1 % and 46.1 %, respectively, at 450 °C. The catalyst’s improved performance in the plasma environment can be attributed to the enhanced metal-support interaction between NiO and the CeO2 NR support, a consequence of the rich surface oxygen vacancy concentration. However, this increase in conversion was accompanied by an escalation in carbon deposition. Considering contributions from the thermal DRM process, the optimal operating temperature was determined as 350 °C. Increasing plasma power at this temperature led to enhanced conversion. However, beyond a threshold of 23.8 W power, the reaction path altered, resulting in reduced syngas output. Increasing the CH4:CO2 feed gas flow ratio, while maintaining constant plasma power and temperature, elevated H2/CO generation. Moreover, increasing the total flow rate under identical conditions, with a constant feed gas flow ratio, reduced both conversions due to decreased chemical residence time. Consequently, under a constant feed gas ratio, a higher syngas yield is achievable with lower overall flow rates.

Modulating internal electric field by oxygen vacancy engineering and consequent forming quantum wells for boosted selective CO2 photoreduction

Although internal electric field of photocatalysts is considered as the potent driving force for efficient charge separation, modulating the internal electric field intensity remains a challenge. Herein, we considered that the internal electric field intensity of Sillén-structured bimetallic oxyhalide PbBiO2Cl could be modulated by tuning surface oxygen vacancy concentration, thereby influencing the corresponding charge transfer. In comparison to bulk PbBiO2Cl and PbBiO2Cl with deficient oxygen vacancies, the PbBiO2Cl with rich oxygen vacancies possessed enhanced internal electric field intensity due to its high oxygen vacancy concentrations, resulting in the primary charge separation spatially. Then the surface oxygen vacancies captured more dissociative electrons as quantum wells to promote the photocatalytic selective CO2-CO conversion. The mechanism was researched and verified by in-situ FTIR and DFT calculations. Using defect engineering to simultaneously modulate internal electric field and form quantum wells for promoting charge separation is an efficient strategy to rationally improve photocatalytic performances.