Hydrothermal Synthesis of Tungsten Oxide Photo/electrocatalysts: Precursor-Driven Morphological Tailoring and Electrochemical Performance for Hydrogen Evolution and Oxygen Reduction Reaction Application

doi:10.21203/rs.3.rs-4836798/v1

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Hydrothermal Synthesis of Tungsten Oxide Photo/electrocatalysts: Precursor-Driven Morphological Tailoring and Electrochemical Performance for Hydrogen Evolution and Oxygen Reduction Reaction Application

https://doi.org/10.21203/rs.3.rs-4836798/v1

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This research examines the effective use of two specific precursor i.e Hydrochloric acid and Oxalic acid used in the synthesis of Tungsten oxide (WO₃). Catalytic reactions including Oxygen Reduction Reaction (ORR) and Hydrogen Evolution Reaction (HER) was investigated with the synthesised material. The morphological as well as electrochemical characteristics were studied using Field Emission Scanning Electron Microscope (FESEM), X-ray Diffraction (XRD), Energy-Dispersive X-ray spectroscopy (EDX), UV spectroscopy along with electrochemical analysis. It is being found that the WO₃ synthesised with oxalic acid (WO₃-ox) demonstrated in superior HER catalysis, whereas the other variant (WO₃ with HCl (WO₃-h)) showed better ORR performance. An optical bandgap of 2.638 eV was obtained for WO₃-ox. Moreover, electrochemical analysis revealed an ORR peak at 0.52 V for WO₃-h, in acidic media of electrolyte. As a result of which the two electrocatalyst were utilised in two different applications. WO₃-ox was used for Methylene Blue (MB) degradation under the UV light and WO₃-h was incorporated as a cathode catalyst for electricity generation and wastewater treatment in Microbial Fuel Cell (MFC). A degradation efficiency of 83.9% was attained in a span of 3 hours. On the other hand, MFC showed superior electrical power density of 209.72 mW/m² with catalyst as compared to bare carbon cloth electrode (139.78 mW/m²). The chemical oxygen demand (COD) removal efficiency, which acts as a measure of wastewater treatment was 1.47 folds higher with the MFC having the catalyst. Thus, by tailored modulation of synthesised material with different precursor can lead to optimization of its features for various applications like degradation of methylene blue and microbial fuel cell.

Tungsten Oxide

Catalysis

Photo/electrocatalyst

Wastewater treatment

Microbial fuel cell

Methylene blue degradation

The exploration of alternate and sustainable energy sources has emerged as a significant area of study in response to the escalating global energy depletion and the environmental consequences associated with conventional energy supplies (Yang et al. 2013). Renewable energy conversion systems (like water electrolysis (Jelinska et al. 2018), fuel cells (Othman et al. 2012)) and storage technologies (battery storage systems (Balamurugan et al. 2023).) utilizes various electrochemical reactions such as Hydrogen Evolution Reaction (HER) and Oxygen Reduction Reactions (ORR). Almost all of them uses active catalysts and thus it becomes important to develop cost effective and highly efficient catalysts to improve the kinetics and overall performance. The noble metal platinum (Pt) is widely recognized as the most effective catalyst for the HER and ORR processes. Nevertheless, the excessive expense, severe scarcity, and inadequate durability of platinum significantly restrict its extensive use (Li et al. 2019). Its notable catalytic activity and enduring stability at minimal overpotentials reduce it an essential constituent in diverse hydrogen production using photoelectrochemical cells for water splitting process (Hansen et al. 2021)(Luo et al. 2019). Moreover, Pt helps in reduction of oxygen into water molecules which acts as a fundamental process in various fuel cells (Yuan et al. 2016). But due to above mentioned obstacles, there is a growing inclination to investigate alternate catalysts that exhibit commensurate or enhanced efficacy in facilitating the HER and ORR. Various non-Platinum group metals (Non-PGM) catalysts were being explored in recent times (Wang 2005).

In recent times, the field of interfacial engineering for electrocatalysts has gained significant attention due to its notable efficiency in enhancing the activity, selectivity, and stability of electrocatalytic processes. Tungsten-based electrocatalysts have garnered considerable interest as viable candidates for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) owing to their inherent availability, environmental compatibility, and noteworthy catalytic activity (Diao et al. 2020). High specific surface area and excellent surface permeability of nanostructured WO₃ make it advantageous in numerous applications. Instant nanorods, 3D nanostructured nanoflowers, and thin films are some of the WO₃ nanostructured morphologies that have been synthesised for water splitting (Bayrak Pehlivan et al. 2021), gas sensing (Park et al. 2012), microbial fuel cell (MFC) (Sharma et al. 2016) and other wastewater treatment applications.

Until the 18th century, water pollution was mostly localised, but as a result of exponential rate of economic development and industrial revolution, wastewater became a necessary by-product of various industries. This wastewater eventually ends up in rivers, ponds, and seas, negatively effecting the ecosystem. Eliminating contaminants such suspended particles, organic carbon, nutrients, and inorganic salts is the primary objective of wastewater treatment in order to protect the environment, aquatic life, and human health. (Wee et al. 2016). Dyes such as methylene blue (MB) are non-biodegradable under natural circumstances, liberated out from industries like paper, textiles etc., which may lead to long-term pollution of marine systems (Oladoye et al. 2022). Photocatalytic degradation of MB using WO₃ has emerged as one of the efficient methods of its removal from the wastewater due to both economic and environmental viability (Maryam et al. 2023). The key degradation reaction of MB with WO₃ as the photocatalyst is described in the reactions below.

$$\:{WO}_{3}+h\nu\:\to\:{WO}_{3}\:\left({e}^{-}+{h}^{+}\right)$$

$$\:{h}^{+}+\:{H}_{2}O\to\:\:\bullet\:OH+\:{H}^{+}$$

$$\:\bullet\:OH+MB\to\:degradation\:products\:({CO}_{2},\:{H}_{2}O,\:etc)$$

Where hυ is the photon energy, $\:{e}^{-}+{h}^{+}\:$is electron hole pair generation, $\:\bullet\:OH$ is the hydroxyl radical responsible in oxidising the MB into less harmful compounds.

In addition to the photocatalytic degradation, MFC technology is becoming a prominent technology that assists in wastewater treatment by providing clean water and electric power. For an extended period, the notion that organic matter can generate electricity through microbial activity has been acknowledged (Lovley 2006). Organic biomass-based bio-electrochemical devices like MFC utilise the microorganism and transforms the chemical energy from the biomass into electrical energy through the catalytic process. The electrons that are generated by the breakdown of organic waste (Solid waste / wastewater) in the anerobic anodic chamber are captured using electrodes and used in the external electrical load connected (Logan 2008). Oxygen as a final electron acceptor in the cathodic chamber of an MFC is an ideal as well as economical choice, but due to high activation energy (498 kJ mol^− 1) it becomes utmost important to incorporate a catalyst to break the O = O bond (Wang et al. 2017). Currently, the device's poor power density and high running costs limit its field applicability. WO₃ has emerged as one of the potential electrocatalyst for ORR application in MFC due to its electronic conductivity, large electrochemically active surface area, resulting in better electrical performance. A maximum power density of 2.75 W/m³ with a COD removal of 81 ± 3% had been observed with WO₃ as cathode catalyst (Das and Ghangrekar 2020). In this research we have synthesised WO₃ with two different precursors to check the performance of the synthesised material for potential uses in various HER and ORR reactions with degradation of methylene blue (MB) and MFC applications respectively.

2.1 Materials:

Sodium Tungstate Dihydrate (product id: 102300733, Sigma Aldrich, > 99%), Sodium Chloride (product id: DD6D660783, Merck), Hydrochloric Acid (product id: 100317, Merck, 35%), Oxalic Acid (product id: 6153-56-6, Thermo Fisher), Nafion™ solution (product id: 31175-20 -9 Alfa Aeser, 5%wt), Ethanol (product id: K48162383 630, Sigma Aldrich), Sodium Sulphate (product id: S0410, RANKEM, 99%), Sulfuric acid (product id:7664-93-9, Merck, 98%) and Potassium Hydroxide pellets (product id:1310-58-3 Merck), are the chemicals used to ensure successful formation and proper characterization of WO₃ using various analytical techniques.

2.2 Hydrothermal Synthesis

The precursor solutions for the synthesis of WO₃ were prepared using two different acids i.e., 2 M Hydrochloric acid and 2 M Oxalic acids. Firstly, 0.825 g of Sodium Tungstate Dihydrate powder (Na₂WO₄.2H₂O) was dissolved in 25 ml of distilled water. Under incessant magnetic stirring at 500 rpm, the pH of the solution was brought down to 2 with the help of either of the above-mentioned acids (HCl and (HCOOH)₂). To enhance the forward reaction 1.16 g of NaCl (0.8 M) was added. The obtained solution was transferred into a PPL-lined 40-mL capacity stainless steel autoclave (PPLAUTO025X, Shilpa Enterprise) and the temperature is maintained at 150°C for 5 hours. The final product was centrifuged and washed with DI water three times and dried for 6 h at 100 ℃. The two powdered materials were labeled as WO₃-ox and WO₃-h for WO₃ synthesised with oxalic acid and hydrochloric acid respectively.

2.3 Characterization.

The morphologies of as-prepared WO₃ nanostructures were analyzed using a Field Emission Scanning Electron Microscope (FESEM) coupled with EDX (ZEISS, SIGMA, Carl ZEISS Microscopy, Germany). The X-Ray diffraction (XRD) analysis was performed on a powder X-ray D8 FOCUS diffractometer (BRUKER AXS, Germany) using Cu Kα radiation λ = 1.54 Å. The UV-Vis absorption spectrum was measured by UV–VIS 1700 recording spectrophotometer (Shimadzu, Japan) creating the baseline using distilled water from 240 nm to 800 nm. The electrochemical analyses were conducted on Autolab potentiostat/galvanostat (PGSTAT128N, METROHM, Switzerland) using a conventional three-electrode cell.

3.1 Morphological Studies

The FESEM analysis was performed to investigate the morphological characteristics of two different WO₃ samples synthesized using two different methods. The FESEM image of WO₃-ox (Fig. 1(a)) showcased a distinct rod-shaped bundle of tightly assembled nanorods with an average length of each rod was about 500 nm. The microscopic analysis of the WO₃-h sample is shown in Fig. 1(b) which revealed a captivating flower-shaped morphology, exhibiting well-defined spikes structures. The observation of outward coming spikes with an average length of 200 nm indicates the presence of elongated protrusions or nanostructures on the surface under investigation. These spikes likely contribute to effective surface area, potentially leading to increased surface reactivity and enhanced material properties. The contrasting morphologies observed in the FESEM analysis provide valuable insights into the influence of different synthesis techniques on the final microstructure of WO₃.

The EDX patterns shown in Fig. 2, revealed that the major elements present in the nanoparticles were Tungsten (W) and Oxygen (O). The atomic weights percentage of the elements for WO₃-ox were found to be as: W = 17.99% and O = 65.90%. Whereas, in case of WO₃-h the atomic wt.% increased for both W (70.64%) and O (70.71%). Along with these a trace amount of Sodium (Na) was detected in the synthesized nanoparticle which may be due to the unwanted residual Na remains from the synthesis process. Overall EDX analysis verified the successful synthesis of the desired WO₃ material with high level of purity.

3.2 XRD Analysis

The powder XRD analysis will offer valuable insights into the crystalline characteristics and crystallographic properties of the synthesized WO₃ nanoparticles. P-XRD of the synthesised sample was carried out in diffractometer using Cu Kα radiation λ = 1.54 Å. Diffraction pattern shown in Fig. 3 confirms the formation of WO₃ (JCPDS Card No. 75-2187), along with that sharp and strong diffraction peaks prove the high degree of crystallization of the material. For WO₃-ox sharp peaks are obtained at 14.06º, 22.9º, 28.15ºand 36.4º corresponding to [100], [001], [200] and [201] lattice parameters respectively. Whereas, for WO₃-h peaks are observed at 2𝛉 values of 13.80º, 22.63º, 27.69º and 36.34º corresponding to [100], [001], [200] and [201] lattice parameters respectively. The aforementioned peaks seen in the WO₃ samples indicated the presence of both hexagonal and monoclinic structures in the synthesised WO₃. The XRD also reveals the broadening of the peaks in case of WO₃-h which may results in smaller crystallite size (Holder and Schaak 2019). Furthermore, the Scherrer formula, which is represented in Eq. 1, was used to determine the material's crystallite size based on the XRD peak broadening.

$$\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:t=\:\frac{0.91\lambda\:}{\beta\:\text{cos}\left(\theta\:\right)}\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(1\right)$$

Where, ‘t’ = crystallite size, ‘λ’ = wavelength of X-Ray ‘β’ = effective full width at half maxima (FWHM). The calculated crystalline size for the maximum intensity peak of most dominant interplanar spacing of [200] plane for both WO₃-ox and WO₃-h was found to be 27.65 nm and 16.59 nm respectively.

3.3 UV-Vis Spectroscopy Analysis:

The absorbance and optical band gap of WO₃ films were measured in the wavelength range of 200-800 nm using a UV-VIS spectrometer. In case of WO₃-ox, a significant absorption peak was attained at a wavelength of 283.57 nm, which signifies the photoactive property of the material in presence of UV light Fig 4 (a). Whereas, no specific absorbance peak was obtained for WO₃-h material Fig 4 (b). The properties of WO₃-h were further analysed using electrochemical method. At the same time, the optical band gap of WO₃-ox was evaluated using Tauc’s plot by taking graph between (αhυ)^1/2 and hυ, with the help of the equation 2.

$$\:{\left({\alpha\:}h\upsilon\:\right)}^{1/2}=\text{A}(h\upsilon\:-{E}_{g})\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\:\left(2\right)$$

(2)

Where, A, α, $\:h\upsilon\:$ and $\:{E}_{g}\:$are constant of proportionality, absorption coefficient, incident energy of the light and optical bandgap respectively. Extrapolating the curve to the x-axis of the Tauc’s plot of WO₃-ox gave the optical band gap of 2.638 eV (Fig. 5).

3.4 Electrochemical Analysis

The electrochemical analysis was carried out in a three-electrode system with material coated on glassy carbon electrode as working electrode, hydrogen electrode as reference electrode and platinum as counter electrode. The experiment was carried out in acidic media i.e., 0.5 M Sulphuric acid (H₂SO₄). The catalyst sample was prepared by adding 5 mg of sample (WO₃-ox & WO₃-h) in 1 ml of ethanol. f was used as a binder. The solution was thoroughly mixed and sonicated for 1 hour. The catalyst material was then deposited on glassy carbon electrode having a surface area of 0.07 cm² using drop casting method.

Cyclic voltammetry (CV) at different scan rates (0.01 V/s – 0.1 V/s) of the both the catalyst in acidic media was carried out (Fig. 6 (a) & (b)). The CV of WO₃-ox showed a steep increase towards the negative current density with an onset potential of 0.1 V, which signifies a Hydrogen Evolution Reaction (HER). A maximum current density of 1.2 mA/cm² was obtained at a potential of -0.5 V. Whereas, in the CV of WO₃-h, an oxygen reduction peak was observed at a voltage of 0.52 V (Fig. 6 (b)). Here we propose that the ORR performance is mainly attributed by outward growing flower-like structure which can easily accumulate electrons, possessing a lower activation energy for the oxygen reduction. At the same time, HER property of WO₃-h was obtained with an onset potential of -0.04 V with a high current density of 10 mA/cm² at a voltage of 0.5 V.

Simultaneously, to check the photo activity of the WO₃-ox, the three-electrode setup was placed inside a UV reactor as shown in Fig. 7 (a). The UV light was turned ON and OFF at an interval of few seconds with a constant voltage of 0.1 V. The maximum current density of 0.42 mA/cm² was obtained when the catalyst was irradiated with a UV light having a wavelength of 253.7 nm and intensity of 0.16 W/m². The spike in the current signifies the catalyst to be photosensitive in UV radiation as shown in Fig .7 (b).

4.1 Methylene blue (MB) degradation

4.1.1 Preparation of sample

The photocatalytic performance of the nanomaterial was evaluated by examining the degradation of MB under ultraviolet radiation. During the test, 100 ml of the aqueous solution of MB (10 mg/L) was taken where 10 mg of the WO₃-ox was suspended. Before starting the experiment, the suspension was subjected to magnetic stirring a dark chamber for 60 minutes to confirm the establishment of the adsorption/desorption equilibrium of MB molecules on the catalyst surface. At a definite interval of 0.5 hr a particular volume of the suspension was taken in vials for the analysis. To recover the photocatalyst the suspension was centrifuged at 12000 rpm for 15 minutes and was poured into cuvettes for the analysis.

4.1.2 Results of MB degradation

The absorbance curve is shown in Fig. 8 confirms the degradation of the methyl blue under UV light. The visible spectroscopy of methylene blue showed a peak at 664 nm. The oxidation of methylene blue could be detected by UV-vis absorption; concurrently, we saw that the colour of the methylene blue changed from dark blue to colorless, suggesting a progressive oxidation over a time span of 3 hours.

The dye degradation efficiency of the sample was determined using the degradation rate calculation formula:

$$\:D=\frac{{C}_{0}-C}{{C}_{0}}\times\:100\%$$

Where, $\:{C}_{0}$ is the concentration of MB at adsorption equilibrium and $\:C$ is the concentration of the solution after the illumination of UV light at a specific time. The synthesised WO₃ catalyst exhibited a photocatalytic performance of 83.9%.

4.2 Wastewater treatment and bio-electricity generation from Microbial Fuel cell (MFC)

4.2.1 Fabrication of MFC

A double chambered MFC was fabricated from plexiglass with each chamber volume of 150 ml separated by the cation exchange membrane (Nafion 117). Cabon cloth having an effective surface area of 28.26 cm² was utilised as electrode in both the cambers in MFC-1 and catalyst was loaded (loading 0.5 mg/cm²) on the carbon cloth on the cathodic-side in MFC-2. The carbon cloth was pretreated firstly with distilled water, followed by 1M H₂SO₄ and lastly again by distilled water. The electrodes were then dried in oven at 100℃. In the experiments kitchen wastewater from the Saraighat CV Raman hostel of Tezpur University was chosen along with 10% inoculum was taken from the outlet slurry of biogas plant of Tezpur University. The slurry was preheated at 100℃ for 20 minutes to inactivate the methanogenic bacterias present in the sample. The MFCs were operated at room temperature in the fed-batch mode. The electrical datas was measured and stored by using a DC electronic load (BK Precision 8600). Current and power densities were determined using Ohm's law as previously mentioned (Khater et al. 2017). Polarisation and power curves were plotted using a single-cycle approach. The pseudo-steady-state voltage was recorded across various external resistances ranging from 7.5 KΩ to 10 Ω.

4.2.2 Performance of MFC

The build-up voltage was measured at a constat external resistance of 7500 Ω where, two additional cycles were introduced once the voltage starts dropping. The measurement was done for a total of approximately 160 hours, where the maximum voltage obtained from MFC-1 was recorded as 0.336 mV, whereas from MFC-2 0.448 mV was obtained, i.e. increase of 33%, as shown in Fig. 9. The correlation between current density with power density and voltage was plotted to understand the electrical performance of the MFC with bare and modified electrodes. As anticipated, MFC-2 with WO₃ on carbon cloth cathode, exhibited superior performance in terms of maximum power density i.e. 209.72 mW/m² in comparison to MFC − 1 (139.78 mW/m²), as can be seen in Fig. 10(b).

This is possible because of increase in ORR active site due to presence of catalyst on the cathode surface. At the same time, internal resistance (IR) of the MFCs were calculated from the polarisation curve by calculating the slope of the graph (Fig. 10 (a)) in the ohmic region (Das and Ghangrekar 2020). It has also become evident that the IR of MFC-1 was found to be 1122 Ω in comparison to MFC-2 with 494 Ω. Table 1 compares the electrical performance of the MFC with different cathode catalysts to the results of the current investigation.

Table 1

Summary of the performances of different MFCs operated using various cathode catalyst materials.
Wastewater	Catalyst	Maximum voltage (V)	Maximum power density (mWm^− 2)	Reference
Domestic	α-MnO₂	0.38	111	(Majidi et al. 2019)
Paper industry	Graphene combined with nitrogen	0.49	99.6	(Estrada-Arriaga et al. 2021)
Sea food processing	Activated carbon	0.68	105	(Jayashree et al. 2016)
Synthetic	Pt/C	0.78	193	(Roche et al. 2010)
Domestic	graphite paste (GP) modified with TiO₂	0.36	85	(Mashkour et al. 2017)
Palm oil mill effluent	Ni/C Pt CuPc/C	0.75 0.87 0.86	94.4 120.8 118.2	(Ghasemi et al. 2013)
Kitchen	WO₃/C	0.44	209.72	This study

Cyclic voltammetry was used to characterise the electrochemical properties of the MFC. It helps in analysing the electrochemical behavior of biocatalysts, including redox catalytic currents, electron discharge (ED), electron transfer to anode, electron neutralization at cathode, and substrate oxidation (Venkata Mohan et al. 2008). In this three-electrode system was used where, the anodic terminal was used as working electrode, cathode terminal as counter electrode and the reference electrode (Ag/AgCl) was set at the anodic chamber. Voltammograms revealed considerable change in the redox peaks and electron transfer mechanism as a consequence of anodic biofilm development by exoelectrogens.

Figure 11 shows the in-situ cyclic voltammetry curve of the microbial fuel cell. In case of MFC-1 the voltammogram chronicled a maximum oxidative current of 7.45 mA along with reduction peak at -0.61 V (vs Ag/AgCl; -3.71 mA) in reverse scan. Whereas, in MFC-2 a maximum current of 15.46 mA (2-fold higher than MFC-1) was obtained. The use of catalyst makes the redox reaction spontaneous hence increase in the oxidative current(Das and Ghangrekar 2020). Moreover, two significant reduction peaks can be depicted from the CV, i.e. at -0.10 V (vs Ag/AgCl; -2.22 mA), which may correspond to redox reaction of certain specific biofilm activity due to the presence of catalyst in the system, which was not observed in MFC-1 and secondly at 0.8 V (vs Ag/AgCl; -8.35 mA). The ORR exhibits increased current owing to its low diffusion resistance to protons, large active surface area of the electrodes.

The influent and effluent of both the MFCs were analysed using the Chemical Oxygen Demand (COD) reduction (Fig. 12), to determine the effectiveness of organic matter removal. The COD was calculated using closed reflux colorimetric method (Clesceri, L.S.; Greenberg, A.E.; Eaton 1999). The COD removal of MFC-1 and MFC-2 was found to be 53.5% and 78.7% respectively (Fig. 13). Coulombic efficiency (CE) was measured to determine the fraction of chemical energy that has been converted into electrical energy using the formula given below:

$$\:CE=\frac{{\int\:}_{0}^{t}Idt}{F{b}_{es}V\frac{\varDelta\:COD}{{M}_{s}}\:}\times\:100$$

Where I is the current generated: M_S is the molecular weight of Oxygen; b is number of electrons exchanged per mole of oxygen; V is the volume of the anodic chamber of the MFC; F is Faraday’s constant i.e. 96485, $\:\varDelta\:COD$ is the change in COD concentration after time t. There has been an increase in the coulombic efficiency due to higher ORR active sites for better electron transfer in MFC-2 after the utilisation of the ORR catalyst. The CE of the MFC-1 was found to be 11% in comparison to MFC-2 as 14%, which is 1.27-fold higher, resulting in overall improved performance of the MFC (Fig. 13).

In summary, well-structured rod and flower shaped WO₃ was synthesised hydrothermally, using (COOH)₂ and HCl respectively. Various characterizations provided the support for the pure synthesis of the catalyst i.e., WO₃-ox & WO₃-h. UV-Vis spectroscopy revealed absorption of UV light by WO₃-ox at 283.57 nm with an optical band gap of 2.638 eV. The electrochemical analysis revealed the occurrence of hydrogen evolution reaction for WO₃-ox whereas, oxygen reduction reaction for WO₃-h. The catalysts were incorporated as the active materials for mainly two applications. WO₃-ox was used for the degradation of the MB and WO₃-h was used as a cathode catalyst in MFC. The oxidation of the MB in presence of suspended WO₃-ox led to treatment of the wastewater with a photocatalytic performance of 83.9% in a time frame of 3 hours. Moreover, the inclusion of WO₃-h in the cathode material of MFC led to enhanced (1.5 folds) electrical performance of MFC. The COD removal percentage of MFC-2 was increased to 78.7% with respect to 53.5% for MFC-1. Thus, it can be concluded that WO₃ holds a great potential for different applications like water splitting specially WO₃-ox catalyst as well as cathode catalyst for microbial fuel cell with WO₃-h, by simply changing the synthesis procedure.

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Author’s Contribution: Both the author has contributed to the study conception and design. Material preparation, data collection and analysis were performed by Rahul Sarma. The first draft of the manuscript was written by Rahul Sarma under the supervision of Biraj Kumar Kakati. Both the authors has read and approved the final manuscript

Funding: No funding was received to assist with the preparation of this manuscript

Competing interest: The authors have no competing interests to declare that are relevant to the content of this article.

Availability of data and materials: Not applicable

Acknowledgement:

The author (Rahul Sarma) would like to acknowledge All India Council for Technical Education (AICTE), Govt of India, for providing financial support as AICTE Doctoral Fellowship (ADF) to the author. The authors would also like to thank Council of Scientific and Industrial Research- North East Institute of Science and Technology (CSIR-NEIST), Jorhat, Assam and Sophisticated Analytical Instrumentation Centre (SAIC), Tezpur University for providing the existing infrastructure for various material characterization facility.

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Editorial decision: Major Revision
20 Sep, 2024
Reviewers agreed at journal
02 Sep, 2024
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30 Aug, 2024
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Hydrothermal Synthesis of Tungsten Oxide Photo/electrocatalysts: Precursor-Driven Morphological Tailoring and Electrochemical Performance for Hydrogen Evolution and Oxygen Reduction Reaction Application

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Abstract

Figures

1 Introduction

2 Materials and Methods for synthesis of WO

2.1 Materials:

2.2 Hydrothermal Synthesis

2.3 Characterization.

3 Results and Discussion

3.1 Morphological Studies

3.2 XRD Analysis

3.3 UV-Vis Spectroscopy Analysis:

3.4 Electrochemical Analysis

4 Application

4.1 Methylene blue (MB) degradation

4.1.1 Preparation of sample

4.1.2 Results of MB degradation

4.2 Wastewater treatment and bio-electricity generation from Microbial Fuel cell (MFC)

4.2.1 Fabrication of MFC

4.2.2 Performance of MFC

5 Conclusion

Declarations

Acknowledgement:

References

Supplementary Files

Status:

Version 1