Efficient photoelectrochemical water splitting and impedance analysis of WO3−x nanoflake electrodes

Solar-powered water splitting with photoelectrochemical (PEC) devices is considered to be a promising method to simultaneously harvest and store solar energy at a large scale. Nanostructured semiconductors offer potential advantages in PEC application due to their large surface area and size-dependent properties, such as increased absorption coefficient, increased band-gap energy and reduced carrier-scattering rate. In this contribution, self-doped tungsten trioxide (WO_3?x) nanoflake arrays were synthesized via a new route which involves the dealloying of Fe–W amorphous alloy, thermal treatment in air and properly cathodic polarization. The effects of different cathodic polarization current leading to different x value in WO_3?x on the morphology, phase, and photoelectrochemical performance of the resultant samples were investigated. It was found that WO_3?x with the appropriate x value presents a dramatic photoelectrochemical current density of 8.7 mA cm^?2 in the presence of methanol as a hole scavenger, five folds larger than that of pristine WO₃ nanoflakes. UV–vis reflection spectra suggest that the light absorption spectrum range of WO_3?x extends from UV to visible light region. Electrochemical impedance spectroscopy disclosed that the unique nanoflake architecture and the surface defects offer improved light harvesting as well as efficient charge transportation.     

Enhanced photoelectrochemical performance of anatase TiO2 by metal-assisted S–O coupling for water splitting

In this study, hybrid density functional theory calculations have been used to investigate the electronic structures of (Mg, S), (2Al, S), (Ca, S), and (2Ga, S) codoped anatase TiO₂, aiming at improving their photoelectochemical performance for water splitting. It is found that the acceptor metals (Mg, Al, Ca, and Ga), assisting the coupling of the incorporated S with the neighboring O in TiO₂, lead to the fully occupied energy levels in the forbidden band of TiO₂, which is driven by the antibonding state π* of the S–O bond. It is also found that the metal-assisted S–O coupling can prevent the recombination of the photo-generated electron–hole pairs and effectively reduce the band gap of TiO₂. Among these systems, the (Mg, S) codoped anatase TiO₂ has the narrowest band gap of 2.206 eV, and its band edges match well with the redox potentials of water. We propose that this metal-assisted S–O coupling could improve the visible light photoelectrochemical activity of anatase TiO₂.     

Role of sputtered WO3 underlayer and NiFeCr-LDH co-catalyst in WO3–BiVO4 heterojunction for enhanced photoelectrochemical water oxidation

WO₃–BiVO₄ (WO-60s/BVO) heterojunction was synthesized by radio-frequency sputtered WO₃ onto FTO substrate, followed by spin-coating of BiVO₄ layer. Furthermore, Cr incorporated NiFe-LDH (NiFeCr-LDH) oxygen evolution reaction (OER) co-catalyst was electrodeposited onto WO-60s/BVO. The sputtered WO₃ underlayer in the WO-60s/BVO facilitated enhanced electron-hole separation and less transient time for the electron to arrive at back contact than conventional spin-coated WO₃ layers. Incorporating Cr into NiFe-LDH increased the electrical conductivity of LDH, which resulted in an enhanced transfer of photogenerated charge-carrier and significant promotion of the OER kinetics. The heterojunction with sputtered WO₃ underlayer and NiFeCr-LDH co-catalyst attained photocurrent density of 4.9 mA cm⁻² at 1.23 V vs. RHE with an IPCE value greater than 56% in the 350–470 nm wavelength range. Moreover, the WO-60s/BVO-NiFeCr photoanode showed only 7% decay in photocurrent after 6 h with H_2, and O₂ evolution of 98 and 47 μmol cm⁻² h, respectively, suggesting high stability for OER.     

Reasonable regulation of kinetics over BiVO4 photoanode by Fe–CoP catalysts for boosting photoelectrochemical water splitting

Photoelectrochemical (PEC) water splitting using earth-abundant semiconductor offer a promising strategy to produce the sustainable clean energy. Herein, we successfully engineered BiVO₄ photoanode with Fe-doped CoP oxygen evolution catalysts (BiVO₄–Fe/CoP) for the first time. Fe/CoP catalysts could significantly break the kinetic limitations of BiVO₄, contributing to the enhanced charge injection efficiencies and charge carrier density. The rational heterostructure has boosted the photocurrent density and incident photon-to-current conversion efficiency (IPCE) to 2.16 mA/cm² and 43% (7 times than that of the bare BiVO₄), respectively. Meanwhile, the BiVO₄–Fe/CoP photoanode also exhibited the desirable long-term stability during PEC water oxidation for 4 h. The results prove the feasibility of BiVO₄–Fe/CoP configuration, which further provided a novel approach towards the development of efficient PEC water oxidation system.     

High-efficiency photoelectrochemical water splitting with heterojunction photoanode of In2O3-x nanorods/black Ti–Si–O nanotubes

Constructing heterojunction was an efficient way to promote photoelectrochemical (PEC) water splitting performance of TiO₂-based nano-photoanode. In this work, we demonstrated the feasible preparation of oxygen vacancies-induced In₂O₃ (In₂O_3-x) nanorods/black Si-doped TiO₂ (Ti–Si–O) nanotubes heterojunction photoanode for enhanced PEC water splitting. Black Ti–Si–O nanotubes were fabricated through Zn reduction of the as-annealed Ti–Si–O nanotubes, followed by In₂O_3-x nanorods coupling by a facile electrodepositing and Ar heat treatment. Solar to hydrogen conversion efficiency of the heterojunction photoanode reached as high as 1.96%, which was almost 10 times that of undoped TiO₂. The improved PEC properties were mainly attributed to co-doping effects of Si and Ti³⁺/oxygen vacancy as well as In₂O_3-x decoration, which resulted in enhanced optical absorption and facilitated separation-transport process of photogenerated charge carriers. Charge transfer process in the composite system and hydrogen production mechanism were proposed. This work will facilitate designing TiO₂-based nano-photoanodes for promoting water splitting by integrating with elements doping, oxygen vacancies self-doping and semiconductors coupling.     

Correlation between microstructural defects and photoelectrochemical performance of 1D Ti–Nb composite oxide photoanodes for solar water splitting

We report on the optimized fabrication of ultrathin wall nanotubes grown on Ti–Nb alloy via anodization in organic-based electrolytes. The nanotubes are vertically aligned with wall thicknesses of 5–8 nm, diameters of 180–200 nm, and lengths of 2–2.8 μm. Raman spectroscopy and glancing angle x-ray diffraction (GAXRD) measurements indicated the formation of composite oxides of anatase TiO₂ and monoclinic Nb₂O₅. The composite oxides showed better stability at elevated temperatures up to 650 ᵒC and with much smaller induced microstrain compared to the TiO₂ counterpart. X-ray photoelectron spectroscopy (XPS) analysis confirmed the composition of the fabricated nanotubes as a mixed TiO₂–Nb₂O₅ composite. Upon their use as photoanodes to split water, the composite TiO₂–Nb₂O₅ NTs showed almost 2-fold increase in the obtained photocurrent compared to that of bare TiO₂ NTs prepared under the same conditions. Moreover, the incident photon to current efficiency (IPCE) of the mixed oxide nanotubes was higher than that of bare TiO₂ with a positive shift towards longer wavelengths, indicating improved electron mobility and charge collection. Hence, the addition of Nb resulted in the formation of thermally stable and photoactive photoanodes for solar fuel production.     

Noble-metal-free Z-Scheme MoS2–CdS/WO3–MnO2 nanocomposites for photocatalytic overall water splitting under visible light

To fabricate an efficient two-component Z-scheme system for visible light induced overall water splitting, CdS/WO₃ nanocomposites, with cubic CdS nanoparticles grown on the surface of hexagonal WO₃ nanorods, were prepared via a facile precipitation of Cd²⁺ with S²⁻ in the presence of pre-obtained hexagonal WO₃ nanorods. MnO₂ and MoS₂, the co-catalysts for O₂ and H₂ generation respectively, were selectively deposited on WO₃ and CdS in the CdS/WO₃ nanocomposites. The resultant MoS₂–CdS/WO₃–MnO₂ composites show photocatalytic activity for overall water splitting under visible light, with an optimized performance observed over 2.0%MoS₂-0.2 CdS/WO₃-1.0%MnO₂. The visible light induced overall water splitting over MoS₂–CdS/WO₃–MnO₂ nanocomposites can be attributed to the presence of a Z-scheme charge transfer pathway in the CdS/WO₃ nanocomposites, ie, the transfer of the photo-generated electrons from the CB of WO₃ to the VB of CdS to recombine with the photo-generated holes through an efficient interface between cubic CdS and hexagonal WO₃. The left photo-generated holes in VB of WO₃ and the photo-generated electrons in CB of CdS therefore can accomplish the water oxidation and water reduction simultaneously, with the assistance of the surface deposited cocatalysts (MnO₂ and MoS₂). This work demonstrated the great potential of fabricating the two-component direct Z-scheme photocatalytic systems for overall water splitting from two semiconductors with a staggered band structure.     

Design of efficient Mn-doped α-Fe2O3/Ti-doped α-Fe2O3 homojunction for catalyzing photoelectrochemical water splitting

To produce clean chemical fuel of hydrogen efficiently, applying photocatalysts for conducting photoelectrochemical water splitting is indispensable. Hematite (α-Fe₂O₃) has been considered as one of the most effective photocatalysts for water oxidation due to excellent visible-light responses, high stability and source abundance properties, but low electrical conductivity and slow oxidation evolution kinetics limit its application. In this study, a novel α-Fe₂O₃ homojunction is constructed via doping Ti and Mn in two layers using two-step hydrothermal synthesis followed by one-step annealing process. Co-doping effect of Ti and Mn in α-Fe₂O₃ and growing sequence of Mn doped α-Fe₂O₃ (Mn:Fe₂O₃) and Ti doped α-Fe₂O₃ (Ti:Fe₂O₃) are also investigated to illustrate the efficient design of Mn:Fe₂O₃/Ti:Fe₂O₃ homojunction. The optimized Mn:Fe₂O₃/Ti:Fe₂O₃ electrode shows the highest photocurrent density of 2.10 mA/cm² at 1.60 V_RHE respectively comparing to those of 0.10, 1.20 and 0.22 mA/cm² for Ti:FeOOH, Ti:Fe₂O₃ and α-Fe₂O₃ electrodes. The outstanding performance of Mn:Fe₂O₃/Ti:Fe₂O₃ homojunction is attributed to the smaller charge-transfer resistance, higher carrier density, and less charge recombination. This work gives a rational design for hematite-based photocatalysts and successfully attains greatly improved photocatalytic ability for water oxidation. Development of homojunction using heteroatom doping in thus verified to be highly applicable on synthesizing promising photocatalysts.     

Fabrication of 0D/1D/2D ZnS–CuS nanodots/GNRs/g-C3N4 heterojunction photocatalyst for efficient photocatalytic overall water splitting

Photocatalytic water splitting has become a significant challenge in modern chemistry. In this process, the rate-determining step is the hydrogen evolution reaction (HER). In the present work, a surface modification approach for graphitic carbon nitride (g-C₃N₄) was applied to improve its photocatalytic HER. 0D ZnS–CuS nanodots were synthesized with the hydrothermal method as a co-catalyst to enhance the capability and stability of water splitting in the presence of visible light irradiation. Also, graphene nanoribbons were synthesized from CNTs unzipping to reduce the energy barrier of HER, improve the HE kinetic, and enhance the catalytic performance of the g-C₃N₄. By using ZnS–CuS/GNRs₍₂₎/g-C₃N₄ photocatalyst, a low onset potential of 130 mV, slight Tafel slope of 41 mV dec^?1, as well as excellent stability of 2000 s was obtained in acidic media. This efficient performance is attributed to the increased visible light absorption level in the proposed photocatalyst and the high stability in electron-hole pairs.     

Visible light driven nanocrystal anatase TiO2 doped by Ce from sol–gel method and its photoelectrochemical water splitting properties

Visible light driven nanocrystal anatase TiO₂ was prepared by doping rare earth element Ce through sol–gel method. UV–Vis diffusion reflectance spectrum indicated its absorption edge extended to about 550 nm, red shifting about 170 nm compared with that without doping. Ce doping TiO₂ showed obvious anodic photocurrent effect for water splitting under visible light irradiation (λ > 420 nm) in photoelectrochemical measurement with three electrodes configuration. Ce doping TiO₂ showed higher photocurrent density than that of without doping TiO₂ under full arc irradiation. Furthermore, the electronic structures for CeO₂ and TiO₂ were analyzed theoretically based on the first principle calculation. As a result, the electronic structure for Ce doping TiO₂ is proposed as the overlap and some degree of hybridization among splitting occupied Ce 4f and unoccupied Ce 4f with O 2p and Ti 3d respectively. The visible light responsive property is mainly due to the transition from O 2p hybridizing with occupied Ce 4f to unoccupied Ce 4f overlapping with Ti 3d.     

Recent trends in development of hematite (α-Fe2O3) as an efficient photoanode for enhancement of photoelectrochemical hydrogen production by solar water splitting

Solar-assisted water splitting using photoelectrochemical (PEC) cell is an environmentally benign technology for the generation of hydrogen fuel. However, several limitations of the materials used in fabrication of PEC cell have considerably hindered its efficiency. Extensive efforts have been made to enhance the efficiency and reduce the hydrogen generation cost using PEC cells. Photoelectrodes that are stable, efficient and made of cost-effective materials with simple synthesizing methods are essential for commercially viable solar water splitting through PEC technology. To this end, hematite (α-Fe₂O₃) has been explored as an excellent photoanode material to be used in the application of PEC water oxidation owing to its suitable bandgap of 2.1 eV that can utilize almost 40% of the visible light. In this study, we have summarized the recent progress of α-Fe₂O₃ nanostructured thin films for improving the water oxidation. Strategic modifications of α-Fe₂O₃ photoanodes comprising nanostructuring, heterojunctions, surface treatment, elemental doping, and nanocomposites are highlighted and discussed. Some prospects related to the challenges and research in this innovative research area are also provided as a guiding layout in building design principles for the improvement of α-Fe₂O₃ photoanodes in photoelectrochemical water oxidation to solve the increasing environmental issues and energy crises.     

Photocatalytic activity of Ag–TiO2-graphene ternary nanocomposites and application in hydrogen evolution by water splitting

TiO₂-graphene (P25-GR, PG) nanocomposite was fabricated with P25 and graphite oxide through a hydrothermal method, and then Ag nanoparticles (Ag NPs) was assembled in P25-GR (Ag-P25-GR, APG) under microwave-assisted chemical reduction. The prepared samples were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscope (SEM), transmission electron microscopy (TEM), photoluminescence spectrum (PL), UV–vis absorption spectrum (UV–vis) and Raman spectrum, respectively. The results showed that Ag NPs were well dispersed on the surface of PG with metallic state. The ternary Ag-P25-GR (APG) nanocomposites possessed the extended light absorption range and more efficient charge separation properties compared to binary P25-GR (PG). Methylene blue photodegradation experiment proved that surface plasmon resonance (SPR) phenomenon had an effect on photoreaction efficiency. The corresponding hydrogen evolution rate of APG prepared with 0.002 M AgNO₃ solution was 7.6 times than pure P25 and 2.7 times than PG in the test condition. The improved photocatalytic performance can be attributed to the presence of GR and SPR effect, leading to the longer lifetime of photo-generated electron–hole pairs and faster interfacial charge transfer rate. This work indicates that the photoactivity of ternary GR-based nanocomposites is superior to the binary one. We expected our work could give a new train of thought on exploration of GR-based nanocomposites.     

Controlled synthesis of W–Co3S4@Co3O4 as an environmentally friendly and low cost electrocatalyst for overall water splitting

Electrochemistry splitting of water is considered to be one of the most fascinating methods to replace traditional chemical fuels. Here, we design a new method to exploit W–Co₃S₄@Co₃O₄ heterostructures. The W–Co₃S₄@Co₃O₄ material was first prepared and grown in situ on nickel foam by a typical hydrothermal and calcination approach. Based on the principle of electronic regulation, the synergistic effect of W and Co metal ions can increase the charge transfer of the electrode, thus significantly prompting the catalytic activity of the electrode. The W–Co₃S₄@Co₃O₄ material present superior catalytic performance for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), and the overpotential at 10 mA cm⁻² is 260 mV and 140 mV, respectively. Notably, W–Co₃S₄@Co₃O₄ catalyst showed excellent water splitting performance under alkaline conditions (cell voltage of 1.63V @10 mA cm⁻²). Density functional theory calculation shows that the existence of the Co₃O₄ material accelerates the rate of hydrogen production reaction, and the existence of the W–Co₃S₄ material promotes the conductivity of the W–Co₃S₄@Co₃O₄ electrode. The synergistic effect of W–Co₃S₄ and Co₃O₄ materials is beneficial to the improvement of the catalytic activity of the electrode. This study provides a novel view for the development of electrodes synthesis and a novel paradigm for the development of robust, better and relatively non-toxic bifunctional catalysts.     

The oxygen-releasing step in the water splitting cycle by MnFe2O4–Na2CO3 system

Investigation of the feasibility of the thermochemical two-step water splitting cycle based on MnFe₂O₄/Na₂CO₃ system is reported. Influence of temperature and carbon dioxide pressure on the oxygen-releasing step was investigated. XRD analysis was applied to obtain phase identification of reacted powders at investigated experimental conditions. Different sodium sub-stoichiometric Na_1−δ(Mn_1/3Fe_2/3)O_2−δ/2 compounds were observed and their structure determined by using Rietveld analysis. Selected experimental conditions permitted to define a T/pCO2$T/p_{{\text{CO}}_{\text{2}}}$ phase diagram, showing different solid phases coexistence regions. Experimental conditions that permit complete regeneration of the initial MnFe₂O₄/Na₂CO₃ mixture were identified (field I in the reported diagram), demonstrating the possibility of full chemical cyclical operation of the system.     

Convex-nanorods of α-Fe2O3/CQDs heterojunction photoanode synthesized by a facile hydrothermal method for highly efficient water oxidation

Morphology controlling and surface modification of semiconductors is the key for efficient photoelectrochemical (PEC) water splitting systems. This work provides a new strategy for achieving morphology control and heterojunction construction simultaneously by one-step hydrothermal method. The α-Fe₂O₃/CQDs heterojunction photoanode with convex-nanorods morphology is successfully prepared by hydrothermal method in CQDs (Carbon Quantum Dots) aqueous contained iron precursor followed by low temperature annealing treatment. Compared with bare hematite photoanode, the α-Fe₂O₃/CQDs photoanode has 8.5 time higher photocurrent density (at 1.23 V vs. RHE) of 0.35 mA cm^?2 and a negative shift of onset potential about 300 mV. The enhanced photoelectrochemical response is attributed to the convex-nanorods which benefit higher absorbance of light and the formed α-Fe₂O₃/CQDs heterojunction, which can efficiently enhance the electron-hole separation and reduce the surface charge recombination. The morphology and properties of the sample were characterized with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fouriertrans form infrared spectroscopy (FTIR), UV–vis spectra, X-ray diffractometry (XRD), X-ray photoelectron spectra (XPS), and photoelectrical measurements.     

Promotion effect of Nb for Cu/CeO2 water–gas shift reaction catalyst by generating mobile electronic carriers

A series of CuO/CeO₂ catalysts doping with Nb₂O₅ were fabricated by co-precipitation method. It is found that the introduction of Nb⁵⁺ will result in the substitution of Ce⁴⁺ with Nb⁵⁺, thus creating mobile electronic carriers in the as-prepared catalysts. The characterization results correlating with the catalytic activity evaluation disclose that the catalyst added with 1 wt. % Nb₂O₅ shows the most mobile electronic carries, certain amount of weak, medium basic sites and enhanced reducibility and chemical adsorption of CO, thus the best catalytic activity for water–gas shift reaction. However, excessive Nb₂O₅ addition prevents the incorporation of Cu²⁺ into CeO₂ lattice and partially covers the surface of CuO and CeO₂, resulting in weaken their reducibility and interaction between them, thus leading to inferior catalytic performance.     

Production of hydrogen by methane catalytic decomposition over Ni–Cu–Fe/Al2O3 catalyst

Catalysts with high nickel concentrations 75%Ni–12%Cu/Al₂O₃, 70%Ni–10%Cu–10%Fe/Al₂O₃ were prepared by mechanochemical activation and their catalytic properties were studied in methane decomposition. It was shown that modification of the 75%Ni–12%Cu/Al₂O₃ catalyst with iron made it possible to increase optimal operating temperatures to 700–750 °C while maintaining excellent catalyst stability. The formation of finely dispersed Ni–Cu–Fe alloy particles makes the catalysts stable and capable of operating at 700–750 °C in methane decomposition to hydrogen and carbon nanofibers. The yield of carbon nanofibers on the modified 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst at 700–750 °C was 150–160 g/g. The developed hydrogen production method is also efficient when natural gas is used as the feedstock. An installation with a rotating reactor was developed for production of hydrogen and carbon nanofibers from natural gas. It was shown that the 70%Ni–10%Cu–10%Fe/Al₂O₃ catalyst could operate in this installation for a prolonged period of time. The hydrogen concentration at the reactor outlet exceeded 70 mol%.     

Novel synthesis of Ti–Fe2O3/MIL-53(Fe) via the in situ process for efficient photoelectrochemical water oxidation

The slow kinetics of water oxidation has become a challenge for photoelectrochemical hydrogen production. Here, a novel organic-inorganic integrated photoanode system was constructed by using MIL-53(Fe) formed during the in-situ etching process as a cocatalyst to modify Ti–Fe₂O₃. The photocurrent density of Ti–Fe₂O₃/MIL-53(Fe) reaches 2.5 mA/cm², 10 times that of bare Ti–Fe₂O₃ at 1.23 V vs. RHE, and the water oxidation photocurrent onset potential shifts 105 mV negatively. Ti–Fe₂O₃/MIL-53(Fe) reaches 52% at 390 nm for IPCE. The excellent photoelectrochemical performance is due to iron oxide clusters boost charge separation and transfer, in-situ etching exposes more reactive sites, and the tight connection reduces interfacial resistance, which greatly accelerates the surface kinetics of Ti–Fe₂O₃. The in-depth understanding is provided for in-situ modification of photoanodes by metal organic frameworks in this work.     

Fabrication of highly efficient water splitting CoxNi1-xTa2O6 (x = 0–1) photocatalysts with high crystallinity and surface nanostructure

Porous Co_xNi_1-xTa₂O₆ mesoporous nanomaterials were synthesized through a sol-gel route using the spray-dried method. They had high photocatalytic activity for water splitting into H₂ and O₂ under visible light. The X-ray diffraction (XRD) patterns of Co_xNi_1-xTa₂O₆ revealed that Co atoms could displace Ni atoms in the NiTa₂O₆ bulk lattice to form a solid solution. A field emission scanning electron microscope (FE-SEM, JSM-6700F) image showed that the microspheres were constructed of irregular nanoparticles randomly stacked to form a mesoporous structure. UV–Vis diffuse reflection spectroscopy (DRS) was used to determinate the band gap changes of Co_xNi_1-xTa₂O₆ samples, which extended towards the visible light region. However, the photocatalytic activity did not have a linear relationship with the band gap, even when the effect of the s urface area was considered. The distortion index of the TaO₆ octahedral lattice was found to be an important influencing factor, and Co_0.8Ni_0.2Ta₂O₆ showed high photocatalytic efficiency with a maximum of 1367 μmol h^?1 g^?1 for H₂ yield, which made it a promising candidate for splitting water.     

Thermochemical hydrogen production using Rh/CeO2/γ-Al2O3 catalyst by steam reforming of ethanol and water splitting in a packed bed reactor

This study is focused on investigating the dual performance of Rh/CeO₂/γ-Al₂O₃ catalyst for steam reforming of ethanol (SRE) and thermochemical water splitting (TCWS) using a packed bed reactor. The catalyst is designed to be thermally stable containing an active phase of Rh and the redox component of CeO₂ for oxygen exchange, supported on γ-Al₂O₃. The catalyst has been characterised by SEM, XRD, BET, TPR, TPD, XPS and TGA before testing in the reactor. The optimal temperature for SRE reaction over this catalyst is between 700 °C and 800 °C to produce high concentrations of hydrogen (~60%), and low CO and CH₄. The selectivity towards CO and CH₄ is higher at low temperatures and drops with rise in reaction temperature. Further, Rh/CeO₂/γ-Al₂O₃ is found to be active for TCWS at relatively low temperatures (≤1200 °C). At temperatures as low as 800 °C, this catalyst is especially found suitable for multiple redox cycles, producing a total of 48.9 mmol/g_cat in four redox cycles. The catalyst can be employed for large number of redox cycles when the reactor is operated at lower temperatures. Finally, the reaction pathways have been proposed for both SRE and TCWS on Rh/CeO₂/γ-Al₂O₃ catalyst.