Photoelectron Spectroscopy Studies Research Articles

Hybrid graphene nanoflakes for electrochemical sensing with multianalyte detection capability

This work illustrates the production of highly electrochemically active graphene by liquid phase exfoliation technique for ultrasensitive electrochemical sensors. An airless high-pressure spray technique was designed to exfoliate bulk natural graphite into nm-scaled flakes (referred as HP50). Transmission electron microscopy, Raman and X-ray photoelectron spectroscopy studies reveal that the HP50 sample has a mixed structure composed of amorphous carbon and a few-layer graphene fraction with high amount of edge plane defects. The HP50 flakes are drop cast on glassy carbon electrodes to test the simultaneous and selective electrochemical detection of hydrogen peroxide, ascorbic acid, and dopamine. In cyclic voltammetry measurements, hydrogen peroxide reduces at −0.2 V vs Ag/AgCl (1 M), while ascorbic acid and dopamine oxidize at 0.1 V vs Ag/AgCl (1 M) and 0.3 V vs Ag/AgCl (1 M), respectively. Linear sweep voltammetry demonstrates high sensitivity (164, 739, and 3357 μA mM−1 cm−2) and low limit of detection (15, 1.7, and 2.1 μM) for the three analytes, respectively. Interference studies confirm a high sensitivity and selectivity towards the different chemical species. The HP50-based multianalyte sensors are also tested against different environmental and commercial samples, illustrating their viability in practical applications.

Soft X-ray Induced Radiation Damage in Dip-and-Pull Photon Absorption and Photoelectron Emission Experiments.

X-ray irradiation can induce chemical reactions on surfaces. In X-ray spectroscopic experiments, such reactions may result in spectrum distortion and are termed radiation damage. In this study, we investigate the X-ray-induced chemical reaction at the partially oxidized copper surface in the settings of the dip-and-pull experiment, a method that generates liquid-solid interfaces for in situ X-ray photoelectron spectroscopy (XPS) studies. In dense water vapor resembling the predipping condition, a series of time-elapsed X-ray absorption spectra acquired in total electron yield mode (TEY-XAS) shows that X-ray exposure causes copper reduction, which follows first-order kinetics and occurs only at the surface shallower than the probing depth of TEY-XAS. At the solid-water interface created by the dip-and-pull method, the chemical reduction of surface copper is also identified by XPS. We conclude that the reduction is driven by the product of water radiolysis, where the reducing solvated electron prevails against the oxidizing OH radical and results in an overall reduction of surface copper ions.

Green and solid state reduction of GO monolayers sandwiched between Arachidic acid LB layers

A novel, single step and environment friendly solid state approach for reduction of graphene oxide (GO) monolayers has been demonstrated, in which, arachidic acid/GO/arachidic acid (AA/GO/AA) sandwich structure obtained by Langmuir-Blodgett (LB) technique was heat treated at moderate temperatures to obtain RGO sheets. Heat treatment of AA/GO/AA sandwich structure at 200 °C results in substantial reduction of GO, with concurrent removal of AA molecules. Such developed RGO sheets possess sp2-C content of ∼69 %, O/C ratio of ∼0.17 and significantly reduced I(D)/I(G) ratio of ∼1.1. Ultraviolet photoelectron spectroscopy (UPS) studies on RGO sheets evidenced significant increase in density of states in immediate vicinity of Fermi level and decrease in work function after reduction. Bottom gated field effect transistors fabricated with isolated RGO sheets displayed charge neutrality point at a positive gate voltage, indicating p-type nature, consistent with UPS and electrostatic force microscopy (EFM) measurement results. The RGO sheets obtained by heat treatment of AA/GO/AA sandwich structure exhibited conductivity in the range of 2–7 S/cm and field effect mobility of 0.03–2 cm2/Vs, which are comparable with values reported for RGO sheets obtained by various chemical/thermal reduction procedures. The extent of GO reduction is determined primarily by proximity of AA molecules and found to be unaltered with either escalation of heat treatment temperature or increase of AA content in sandwich structure. The single-step GO reduction approach demonstrated in this work is an effective way for development of RGO monolayers with high structural quality towards graphene-based electronic device applications.

Exploring 1T/2H MoS2 Nano Coral Structured Active Electrodes for Enhanced Pseudocapacitive Supercapacitors: A Rigorous Evaluation and Characterization Study

This article optimizes the synthesis parameters of nano coral structured (NC-S) molybdenum disulfide (MoS2) using hydrothermal method and enhances its physiochemical properties for high-performance supercapacitors (SC). This nano coral architecture of transition metal dichalcogenides has garnered significant attention for efficient pseudocapacitive charge storage in SC. Herein, this work demonstrates the fabrication of dual phase MoS2 by tailoring the reaction time of the NC-S. Furthermore, this effect has been explained with the help of several analytical techniques. The synthesized 1T/2H MoS2 NC-S phase was affirmed by powder X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy studies. The field emission scanning electron microscope and transmission electron microscope images unveiled nano corals like morphology with numerous active sites. Impressively, the as prepared 24, 36 and 48 h MoS2 NC-S entrenched as working electrode endows the achievement with a greater specific capacitance of about 761.82, 1550.86 and 1036.28 F/g at 1 A/g of current density manifests an outstanding rate capability of 94.5, 96.5 and 95.3% capacitive retention even after 1000 cycles. Among them, the 36 h (A-36) synthesized NC-S MoS2 possess high specific energy (43.61 Wh/kg) and power (225.50 W/kg) for this application. Additionally, it demonstrates a commendable capacitive retention of 97% for the two-cell asymmetric setup, even after 5000 cycles at 10 A/g of current density. This inventive configuration of a two-cell device is employed using a Swagelok setup, where the 1T/2H phase MoS2 NC-S//AC exhibit outstanding storage stability and sustained up to 180 sec. The promising results validate that this material can significantly enhance performance in energy storage applications.

Improved ammonia gas adsorption of surface engineered WS2 nanoflakes

Recent investigations into nanostructured WS2 have shown promising results in the detection of reducing gases, such as ammonia. However, this material faces limitations with respect to the vital parameters such as sensitivity, recovery, and repeatability over an extended period in its purest form. To address these challenges, a low-energy (5 keV) argon ion beam was used to irradiate nanostructured WS2 nanoflakes at various fluences, leading to observable morphological and structural changes. The irradiation of WS2 resulted in a significant enhancement in its ability to detect ammonia gas. The sensing response saw a threefold increase, and both the response and recovery times were reduced significantly compared to pristine samples. Ion beam irradiation changes the overall morphology of nanoflakes and induces a certain degree of defects as apparent from electron microscopy, X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy studies. The ion-solid interaction simulation predicts a larger amount of sulfur vacancy than tungsten due to irradiation, which is also supported by experimental results. Density functional theory predicts that sulfur vacancy leads a decisive role in better adsorption of ammonia than the pristine surface. The NH3 molecule orients towards the defective surface leading to a higher charge transfer from the NH3 molecule to the surface than the pristine surface along with a smaller adsorption height.

Optimizing charge transport and band-offset in silicon heterojunction solar cells: impact of TiO2 contact deposition temperature

Carrier selective contacts are a primary requirement for fabricating silicon heterojunction solar cells (SHSCs). TiO2 is a prominent carrier selective contact in SHSCs owing to its excellent optoelectronic features such as suitable band offset, work function, and cost-effectiveness. Herein, we fabricated simple SHSCs in an Al/TiO2/p-Si/Ti/Au device configuration. Ultrathin 3 nm TiO2 layers were deposited onto a p-type silicon substrate using the atomic layer deposition method. The deposition temperature of TiO2 layers varied from 100 °C to 250 °C. X-ray photoelectron spectroscopic studies suggest that deposition temperature highly affects the chemical states of TiO2 and reduces the formation of defective state densities at the Fermi energy. The optical band gap values of TiO2 layers are also altered from 3.13 eV to 3.27 eV when the deposition temperature increases. The work function tuning from −5.13 eV to −4.83 eV has also been observed in TiO2 layers, suggesting the variation in Fermi level tuning, which arises due to changes in carrier concentrations at higher temperatures. Several device parameters, such as ideality factor, trap density, reverse saturation current density, barrier height, etc, have been quantified to comprehend the effects of deposition temperature on photovoltaic device performance. The results suggest that the deposition temperature significantly influences the charge transport and device performance. At an optimum temperature, a significant reduction in charge carrier recombination and trap state density has been observed, which helps to improve power conversion efficiency.

A versatile sample-delivery system for X-ray photoelectron spectroscopy of in-flight aerosols and free nanoparticles at MAX IV Laboratory.

Aerosol science is of utmost importance for both climate and public health research, and in recent years X-ray techniques have proven effective tools for aerosol-particle characterization. To date, such methods have often involved the study of particles collected onto a substrate, but a high photon flux may cause radiation damage to such deposited particles and volatile components can potentially react with the surrounding environment after sampling. These and many other factors make studies on collected aerosol particles challenging. Therefore, a new aerosol sample-delivery system dedicated to X-ray photoelectron spectroscopy studies of aerosol particles and gas molecules in-flight has been developed at the MAX IV Laboratory. The aerosol particles are brought from atmospheric pressure to vacuum in a continuous flow, ensuring that the sample is constantly renewed, thus avoiding radiation damage, and allowing measurements on the true unsupported aerosol. At the same time, available gas molecules can be used for energy calibration and to study gas-particle partitioning. The design features of the aerosol sample-delivery system and important information on the operation procedures are described in detail here. Furthermore, to demonstrate the experimental range of the aerosol sample-delivery system, results from aerosol particles of different shape, size and composition are presented, including inorganic atmospheric aerosols, secondary organic aerosols and engineered nanoparticles.

Salicylic Acid-Modified Sm-TiO2 for Photoluminescence and Photocatalysis under Real Sunlight: Synergistic Effects between Ligand-to-Metal Charge Transfer (LMCT) and Sm3+ Dopant.

A salicylic-acid (SA)-modified samarium-doped TiO2 complex (Sm-TiO2/SA) was synthesized via a sol-gel method followed by impregnation. A Raman Fourier transform IR and X-ray photoelectron spectroscopic study showed that SA (as an electron donor) forms a surface complex on the Sm-TiO2 surface through its phenolic/carboxylic functional groups. In the Sm-TiO2/SA complex, a ligand-to-metal charge transfer (LMCT) is active, inducing a marked red-shift in the absorption spectrum of TiO2, which extends to 550-600 nm. The synergetic effect between the LMCT process and the luminescent properties of the lanthanide ions (Sm3+) is discussed and supported by the photoluminescence spectra. Further photocatalytic experiments (under sunlight) and the study of the effect of different scavengers show the presence of competitive reactions between de-ethylation and cleavage of Rhodamine B (RhB) during its degradation. With the Sm-TiO2/SA complexes, the superoxide radical ion (O2 •-) is the main active species responsible for the N-de-ethylation pathway under sunlight irradiation. The cleavage of RhB by the hydroxyl radical (•OH) appears, instead, to dominate with the Sm-TiO2 photocatalysts.

Reversible Optical Switching of Polyoxovanadates and Their Communication via Photoexcited States.

The 2-bit Lindqvist-type polyoxometalate (POM) [V6O13((OCH2)3CCH2N3)2]2- with a diamagnetic {V6O19} core and azide termini shows six fully oxidized VV centers in solution as well as the solid state, according to 51V NMR spectroscopy. Under UV irradiation, it exhibits reversible switching between its ground S0 state and the energetically higher lying states in acetonitrile and water solutions. TD-DFT calculations demonstrate that this process is mainly initialized by excitation from the S0 to S9 state. Pulse radiolysis transient absorption spectroscopy experiments with a solvated electron point out photochemically induced charge disproportionation of VV into VIV and electron communication between the POM molecules via their excited states. The existence of this unique POM-to-POM electron communication is also indicated by X-ray photoelectron spectroscopy (XPS) studies on gold-metalized silicon wafers (Au//SiO2//Si) under ambient conditions. The amount of reduced vanadium centers in the "confined" environment increases substantially after beam irradiation with soft X-rays compared to non-irradiated samples. The excited state of one POM anion seems to give rise to subsequent electron transfer from another POM anion. However, this reaction is prohibited as soon as the relaxed T1 state of the POM is reached.

Reversible oxidation of ethylene on ferroelectric BaTiO3(001): An X-ray photoelectron spectroscopy study

Adsorption and desorption of ethylene on BaO-terminated (001) barium titanate are investigated by X-ray photoelectron spectroscopy. Carbon is found in an oxidized state, at a binding energy similar to that resulting from CO adsorption on BaTiO3(001). The amount of carbon adsorbed on the surface is also similar to the case of CO/BaTiO3(001). Upon heating the substrate up to the loss of its ferroelectric polarization, the C 1s signal from the oxidized spectral region vanishes. At the same time, there was no noticeable oxygen depletion of the surface after repeated C2H4 adsorption and desorption. The substrate remains stable after repeated oxidative adsorption and desorption of ethylene. Desorption occurs at different temperatures, depending on the adsorption temperature, which suggests different adsorption geometries: non-dissociated adsorption at high temperature with ethylene bond on two surface oxygen atoms, and locally dissociated adsorption at lower temperatures, in “formaldehyde-like” local configurations.

Effect of temperature on the stability and performance of III-nitride HEMT magnetic field sensors

The study aimed to investigate the underlying physics limiting the temperature stability and performance of non-surface passivated Al0.34Ga0.66N/GaN Hall effect sensors, including contacts, under atmospheric conditions. The results obtained from analyzing the microstructural evolution in the Al0.34Ga0.66N/GaN Hall sensor heterostructure were found to correlate with the electrical performance of the Hall effect sensor. High-resolution x-ray photoelectron spectroscopy studies revealed the signature of surface oxidation in the GaN cap layer, as well as a slight out-diffusion of “Al” from the AlGaN barrier layer. To prevent the formation of a bumpy surface morphology at the Ohmic contact, we investigated the impact of “Pt” top Ohmic contacts. The application of a top “Pt” contact stack resulted in a smooth Ohmic contact surface and provided evidence that the bumpy surface morphology in Au-based Ohmic contacts is due to the formation of an Al-Au viscous alloy during rapid thermal annealing. In the early stages of thermal aging, the small drop in contact resistivity stabilized with subsequent thermal aging past the initial 550 h at 200 °C. The outcome is that the Al0.34Ga0.66N/GaN Hall effect sensors, even without surface passivation, exhibited a stable response to applied magnetic fields with no sign of significant degradation after 2800 h of thermal aging at 200 °C under atmospheric conditions. This observed stability in the Hall sensor without surface passivation can be attributed to a self-imposed surface oxidation of the cap layer during the early stages of aging, which serves as a protective layer for the device during subsequent extended periods of thermal aging at 200 °C.

Electronic Structure and Surface Chemistry of BaZrS3 Perovskite Powder and Sputtered Thin Film.

Chalcogenide perovskites exhibit optoelectronic properties that position them as potential materials in the field of photovoltaics. We report a detailed investigation into the electronic structure and chemical properties of polycrystalline BaZrS3 perovskite powder by X-ray photoelectron spectroscopy, complemented by an analysis of its long- and short-range geometric structures using X-ray diffraction and X-ray absorption spectroscopy. The results obtained for the powdered BaZrS3 are compared to similar measurements on a sputtered polycrystalline BaZrS3 thin film prepared through rapid thermal processing. While bulk characterization confirms the good quality of the powder, depth-profiling achieved by photoelectron spectroscopy utilizing Al Kα (1.487 keV) and Ga Kα (9.25 keV) radiations shows that, regardless of the fabrication method, the oxidation effects extend beyond 10 nm from the sample surface, with zirconium oxides specifically distributing deeper than the oxidized sulfur species. A hard X-ray photoelectron spectroscopy study on the powder and thin film detects signals with minimal contamination contributions and allows for the determination of the valence band maximum position with respect to the Fermi level. Based on these measurements, we establish a correlation between the experimental valence band spectra and the theoretical density of states derived from density functional theory calculations, thereby discerning the orbital constituents involved. Our analysis provides an improved understanding of the electronic structure of BaZrS3 developed through different synthesis protocols by linking it to material geometry, surface chemistry, and the nature of doping. This methodology can thus be adapted for describing electronic structures of chalcogenide perovskite semiconductors in general, a knowledge that is significant for interface engineering and, consequently, for device integration.

Low cobalt single atoms loading on N-doped carbon for high Na storage performance

Cobalt single atoms on nitrogen-doped carbon (CoSAs/N-C) were successfully synthesized through the pyrolysis of metal-organic supramolecular self-template. Only 0.12 wt% metal-doped CoSAs/N-C anodes bring a rate capacity enhancement of 195 mAh g−1 compared to the blank group of nitrogen-doped carbon electrodes at 0.1 A g−1. In addition, the CoSAs/N-C anodes exhibit remarkable sodium-ion storage capacities of 285 mAh g−1 after 2000 cycles at 1.0 A g−1 and 133 mAh g−1 with an exceptional cycling stability for 10,000 cycles at an ultra-high current density of 20 A g−1, thereby showcasing excellent Na ion storage performance. Ex-situ X-ray photoelectron spectroscopic study demonstrates that some N atoms in CoSAs/N-C can reversibly store and release Na ions during discharge and charge cycles. The full cell assembled with CoSAs/N-C anode and Na3V2(PO4)3 cathode displays Coulombic efficiency of >99.7 % after 200 cycles at 0.5 A g−1. Density functional theory (DFT) calculations further reveal that the presence of single-atom Co results in a decrease in the Na binding energy surrounding pyrrolic-N and pyridinic-N structures. This moderate binding energy may be beneficial for Na ion adsorption and desorption. This study opens up new possibilities of fabricating advanced metal single atom anodes for high-performance sodium-ion batteries.

Green synthesis of Vitis vinifera extract-appended magnesium oxide NPs for biomedical applications

Abstract Biologically active magnesium oxide (MgO) nanoparticles were synthesised using green reduction with an extract derived from the Vitis vinifera plant. The investigation focused on examining the structure and carbon abundance resulting from the thermal degradation of adsorbed biomolecules. It was accomplished using powder X-ray diffraction, Raman spectroscopy, and FT-IR analysis techniques. X-ray photoelectron spectroscopy studies conducted on MgO nanoparticles indicate the absence of any supplementary peaks, thereby indicating the purity of the material. The morphological characteristics, which have been examined using field emission scanning electron microscopy and TEM methodologies, demonstrate the presence of particles with a spherical shape, exhibiting minimal agglomeration and a uniform distribution across the surfaces of MgO. The porous structure, porosity, and pore volume of the MgO particles were evaluated using Brunauer-Emmett-Teller surface analysis. The experimental findings reveal that the surface area of the MgO nanoparticles is 23.8742 m2/g, while the total pore volume is 0.12528 cm3/g. Additionally, the average pore diameter is determined to be 1.7 nm. These observations collectively suggest the presence of microporous structures within the MgO nanoparticles. This article discusses the biological studies to assess the antibacterial, antifungal, anti-inflammatory, and anti-diabetic activities of the synthesised MgO nanoparticles.

CTAB-facilitated ex-situ synthesis of chitosan-based ZnO, CuO, and ZnO/CuO nanocomposites for improved optical emission

The present investigation deals with the synthesis and characterization of CTAB assisted pristine ZnO, CuO and ZnO/CuO nanoparticles and their corresponding chitosan based nanocomposites. The XRD and FTIR results reflect the successful formation of pristine nanoparticles as well as their chitosan nanocomposites. The X-ray photoelectron spectroscopy (XPS) study confirms the tagging of chitosan by revealing the presence of element nitrogen which is expected to be derived from the chitosan biopolymer itself. The optical investigation reveal the bandgap energy of the pristine ZnO, CuO and ZnO/CuO nanoparticles to be 3.2, 1.95 and 2.60 eV, respectively. The interaction of chitosan with the pristine samples bring in changes in the bandgap energy due to alterations in energy band structure. The photoluminescence (PL) studies also clearly indicate the improved optical and electronic property of the composites on addition of chitosan by introducing defects in the crystal structure.

Effect of N Atom Substitution on Electronic Resonances: A 2D Photoelectron Spectroscopic and Computational Study of Anthracene, Acridine, and Phenazine Anions.

The accommodation of an excess electron by polycyclic aromatic hydrocarbons (PAHs) has important chemical and technological implications ranging from molecular electronics to charge balance in interstellar molecular clouds. Here, we use two-dimensional photoelectron spectroscopy and equation-of-motion coupled-cluster calculations of the radical anions of acridine (C13H9N-) and phenazine (C12H8N2-) and compare our results for these species to those for the anthracene anion (C14H10-). The calculations predict the observed resonances and additionally find low-energy two-particle-one-hole states, which are not immediately apparent in the spectra, and offer a slightly revised interpretation of the resonances in anthracene. The study of acridine and phenazine allows us to understand how N atom substitution affects electron accommodation. While the electron affinity associated with the ground state anion undergoes a sizable increase with the successive substitution of N atoms, the two lowest energy excited anion states are not affected significantly by the substitution. The net result is that there is an increase in the energy gap between the two lowest energy resonances and the bound ground electronic state of the radical anion from anthracene to acridine to phenazine. Based on an energy gap law for the rate of internal conversion, this increased gap makes ground state formation progressively less likely, as evidenced by the photoelectron spectra.

Cryogenic Photoelectron Spectroscopic and Theoretical Study of the Electronic and Geometric Structures of Undercoordinated Osmium Chloride Anions OsCln- (n = 3-5).

A series of anionic transition metal halides, OsCln- (n = 3-5), have been investigated using a newly developed, home-constructed, cryogenic anion cluster photoelectron spectroscopy. The target anionic species are generated through collision-induced dissociation in a two-stage ion funnel. The measured vertical detachment energies (VDEs) are 3.48, 4.54, and 4.81 eV for n = 3, 4, and 5, respectively. Density functional theory calculations at the B3LYP-D3(BJ)//aug-cc-pVTZ(-pp) level predict the lowest energy structures of the atomic form of OsCln- (n = 3-5) to be a quintet triangle, quartet square, and quintet square-based pyramid, respectively. The CCSD(T)-calculated VDEs and corresponding adiabatic detachment energies agree well with our experimental measurements. Analysis of the corresponding frontier molecular orbitals and charge density differences suggests that the d-orbitals of the transition metal Os play a primary role in the single-photon detachment processes, and the detached electrons originating from different molecular orbitals are distinguishable.

Exploring the Use of Fe2.5Ni2.5Sn3 as a Monolithic Catalyst for Oxygen Evolution Reaction Under Alkaline Conditions

Abstract Enabling a hydrogen fuel-based economy is reliant on the discovery of materials that catalyze the electrolysis of water which requires low-cost catalytic electrodes to improve the kinetics of the oxygen evolution reaction. Fe2.5Ni2.5Sn3, was prepared by arc-melting and electrochemical studies were conducted to evaluate its ability to catalyze the oxygen evolution reaction. Potentiodynamic polarization testing revealed that the Fe2.5Ni2.5Sn3 alloy had a Tafel slope of 40 mV/decade and required an overpotential of 326 mV in order to obtain a current density of 10 mA/cm2. X-ray photoelectron spectroscopy studies indicated that the native oxide present on the surface became hydrated upon subjecting it to oxygen evolution studies.

ZnO nanorods on POPD/GCN/TCFP with ternary synergy for promoting electro-oxidation of furfuryl alcohol

In this work, Poly(o-phenylenediamine) (POPD) and zinc oxide (ZnO) nanoparticles were electrochemically deposited on GCN (graphitic carbon nitride) coated TCFP (Toray carbon fiber paper) electrode. The modified electrode ZnO-POPD-GCN-TCFP was assessed by Field emission scanning electron microscopy (FESEM), X-ray diffraction analysis (XRD), and X-ray photoelectron spectroscopy (XPS) studies. The electrochemical studies were carried out via cyclic voltammetry (CV) and electrochemical impedance spectroscopic (EIS) methods. The developed electrode was employed for the oxidation of furfuryl alcohol (FA) using 4-ACT (4-acetamido TEMPO) as a mediator in an alkaline medium via bulk electrolysis. Proton nuclear magnetic resonance (1H NMR) spectroscopy was used to characterize the final product. The oxidation of FA to furfural was accelerated by the heterogeneous catalyst ZnO-POPD-GCN-TCFP electrode owing to its good electrocatalytic activity and stability. Hence, a sustainable electrochemical method for synthesizing furfural, with significance in the realm of green chemistry, was developed. The Electro-oxidation of FA offers a clean alternative to traditional methods utilizing electricity, potentially from renewable sources, to drive the reaction, reducing reliance on harsh chemicals and minimizing environmental impact. By adjusting parameters like electrode potential and electrolyte composition, it is possible to optimize the reaction conditions for furfural production with optimal yield, which has several applications in daily life.

Incorporation of atomic Fe-oxide triggers a quantum leap in the CO2 methanation performance of Ni-hydroxide

The heterogeneous catalytic conversion of carbon dioxide (CO2) to methane (CH4) via CO2 methanation offers a promising avenue for establishing the closed carbon loop. Nevertheless, the lack of effective catalysts limits its industrial applications. Considering this, we developed a novel heterogeneous catalyst comprising oxygen vacancies enriched atomic Fe-oxide clusters confined in the TiO2-supported Ni-hydroxide (denoted as NiFe-TiO2) via wet chemical reduction method. This material delivers an unprecedently high CH4 productivity of ∼24,358 mmol g-1h−1 in CO2 methanation at 300 °C, surpassing the Ni-TiO2 (12,481 mmol g-1h−1) by ∼ 95 %. On top of that, the high structural reliability of the Fe-oxide atomic clusters endows the NiFe-TiO2 catalyst with outstanding durability, where it achieves an optimum CH4 productivity of ∼ 36,399 mmol g-1h−1 after 116 cycles (155 h) with CH4 selectivity of 90.5 % and retains the pristine performance up to 220 cycles (330 h) in the stability test. With evidence from in-situ X-ray absorption and ambient pressure X-ray photoelectron spectroscopy studies, the performance descriptors and reaction pathways were unveiled, where the oxygen vacancies in the atomic Fe-oxide clusters and the adjacent Ni-hydroxide domains synergistically boost the CO2 activation and the H2 dissociation, respectively. Such a potential synergy enables the simultaneous operation of all intermediate steps for enhanced CO2 methanation kinetics on the NiFe-TiO2 surface. Most importantly, these findings not only unravel the merits of oxygen vacancies in transition metals for CO2 methanation but mark a step ahead for the rational design of heterogeneous catalysts in various catalytic applications.