Development of Bifunctional Oxygen Electrocatalysts Using Solution Combustion Synthesis For Fuel Cell Applications

Advanced energy storage and conversion systems such as fuel cells and metal air batteries achieved wide attention. Oxygen reduction reaction (ORR) and Oxygen evolution reaction (OER) are the prominent reactions that govern the charging and discharging capability of batteries as well as fuel cells. The bifunctional electrocatalyst that can be used to activate both the reactions (ORR and OER) are demanding and still challenging. Platinum (Pt) group metals are found to be the most efficient electrocatalyst, but their high cost and limited availability restrains large scale commercialization. Intensive research focused on developing highly active, costeffective and earth abundant materials for bifunctional oxygen electrocatalyst for next generation energy sources. In this work, we mainly focused on the solution combustion synthesis (SCS) method for preparing nanoparticles and studying their bifunctional electrocatalytic performance in alkaline medium. The structure, physio-chemical nature and composition of the material can be tuned by the synthesis condition that enables us to correlate them with the catalytic performance for oxygen reactions. In SCS technique, the fuel to oxidizer ratio (φ) is identified as a critical parameter affecting the properties of the synthesized nanoparticles. In the first part of this study, we prepare cobalt nanoparticles with different fuel ratio (φ = 0.5, 1 and 1.5). Then we synthesized bimetallic Ag-M (Cu and Co) using three different modes of SCS. The phase distribution of the catalyst after stability shows a clear phase de-alloying and segregation of elements that reduces the performance. Thereafter, we focused on perovskite materials LaMO3 (M = Cr, Mn, Fe, Co, Ni) with stable and homogeneous perovskite phases. LaMnO3 shows the maximum current density for ORR, whereas LaCoO3 shows best performance for OER. Finally, we focused on enhancing the surface area of perovskite by incorporating a leachable salt (e.g. KCl) during combustion that breaks down the three-dimensional crystalline structure to restrict post combustion agglomeration and sintering, which in-turn translates into better electrocatalytic performance. Based on these results, we conclude that the salt assisted SCS has the potential for preparing highly efficient and durable bifunctional electrocatalyst suitable for fuel cells and metal air batteries

Hydrogen Production via Ethanol Decomposition over Bimetallic Catalyst

Bimetallic catalyst shows distinct physical and chemical properties differ from its monometallic catalyst due to the high synergy between the monometals. Bimetals of transition metals shows different applications in the field of catalysis, batteries and solar energy conversion etc. CuCo bimetallic catalysts are excellent candidate for the applications in the field of heterogeneous catalysis, solid state sensor, energy storage devices, and lithium-ion batteries. With the increase in fuel cell application, need of H2 source also rises. H2 can be extracted from the hydrogen rich precursors of light alcohol such as methanol and ethanol that can be produced from corn stover, starch containing materials and other biomass byproducts. Ethanol is low toxic and easy handling renewable source for H2 production for fuel cell applications and the production of ethanol is environmentally sustainable. Transition metal possess high C-C cleavage bond which is an indispensable property in ethanol conversion. Steam reforming, partial oxidation, dehydrogenation and decomposition are the main routes for the hydrogen generation from ethanol. Out of these, decomposition technique is a low temperature process and suitable for small scale fuel cell applications e.g. charging cell phones, computers etc. We follow decomposition route for H2 production along with other necessary byproducts. Bimetallic CuCo catalyst shows good performance during ethanol decomposition for hydrogen production in the temperature range of 50°C-400°C. Various physical and chemical techniques (such as thermal method, precipitation methods, pyrolysis process, sonochemical method, polyol method, microwave irradiation, sol-gel process, combustion method etc.) have been reported for the synthesis of different morphological structures of bimetallic nanoparticles In this work we are following combustion synthesis method to prepare cobalt catalysts which have been reported to be active for ethanol-hydrogen production. This work focuses primarily on understanding the reaction mechanism leading to various products using in situ DRIFTS studies. Combustion synthesis was opted for synthesis due to various advantages such as low energy requirement, single step, fast and economic synthesis process as it does not require expensive equipment. In Solution Combustion Synthesis (SCS) the precursors were mixed to form a homogenous solution and heated it over the hotplate heater to initiate the combustion process which resulted in the synthesis of nanoparticles with uniform properties. Typically, it consist a redox reaction of the homogeneous mixture of metal nitrate (oxidizing agent) and oxygen containing fuels (reducing agent) such as glycine, urea, glucose, citric acid etc. The reaction between NH3 and HNO3 released during decomposition of glycine and metal nitrate respectively produces the energy required for single step combustion synthesis. At higher value of φ, the reactive medium generates H2 rich reducing environment to convert metal oxide to metallic form Bimetallic CuCo were synthesized from the aqueous solution of cobalt nitrate (Co(NO3)2·6H2O), copper nitrate (Cu(NO3)2·6H2O) and glycine (C2H5NO2) in solution combustion synthesis (SCS) method using a fuel to oxidizer ratio of φ 0.5, 1, 1.75 and 2.5. The amount of precursors was calculated based on the synthesis of 1.5 g product in the output. These precursors were mixed in 75 ml of water and stir continuously for 1 hr to form a homogenous mixture. The solution was heated over a hot plate heater until all the water got evaporated. Once it reaches the ignition temperature, the combustion reaction started locally at one point and then spread inside the beaker. The resulted powder was grinded using a mortar and pestle to get a uniform powder to be used for catalytic investigations. Synthesized particles were characterized using XRD, SEM and TEM. Ethanol decomposition over bimetallic CuCo were conducted using in situ diffuse reflectance infrared fourier transform spectroscopy (DRIFT) study under N2 flow at different temperatures (50, 100, 200, 300, 400°C). Temperature-time profile of CuCo shows an increase in combustion temperature with increase in fuel ratio with maximum temperature at φ = 1 (stoichiometric ratio) and after that it decreases. The XRD shows the presence of copper-cobalt component in their oxidized states. Theoretical studies shows increase in particle size with maximum flame temperature. Crystalline size calculation using Scherrer formula shows the same trend in particle size calculation as in Table 1. SEM of as-synthesized nanoparticles of cobalt oxide at different molar ratios from 0.5 to 2.5 in SCS mode shows the nanoparticles of high porosity that are randomly distributes as well as agglomerated. Mostly this high porosity is due to the escaping of excess gases during combustion process. Also the EDS results are in consistent with the XRD results showing higher amount of oxide in the synthesized CuCo compound. TEM image in Fig. 1 also shows agglomeration that is common in solution combustion mode with non-uniform sized particles. Copper-cobalt oxide synthesized using combustion technique has been reduced to pure nanocrystal by passing hydrogen in the reaction chamber at 300°C. An FTIR spectrum at 50 and 100°C shows the presence of adsorbed ethanol and ethoxy species over the reduced catalyst. IR band at 3669 cm− 1 indicates the presence of OH from adsorbed ethanol on the catalyst surface. At higher temperature the molecularly adsorbed ethoxy species is converted into acetate species along with the presence of carbonate species. After increasing the temperature from 200°C the intensity CO2 band at 2335-2367 cm− 1 is evident. At this temperature the acetate species are dehydrogenated to acetaldehyde and other intermediate species. Strong acetate band of 1760 cm− 1 above 200°C could be due to the transformation of acetaldehyde formed by the dehydrogenation of ethanol to either ethyl acetate or acetic acid though the nucleophilic reaction of ethoxy or hydroxyl species with the surface aldehyde. The presence of IR band between 2830-2695 cm− 1 shows the presence of aldehyde group in the decomposition reaction. At higher temperature, the presence of carbonate species is evident with the carbonate layer formation from SEM and TEM images. This carbon layer at higher temperature hinders the action of catalyst in ethanol decomposition reaction.qscienc

A comprehensive and critical review on recent progress in anode catalyst for methanol oxidation reaction

The synthesis of anode electrocatalyst with high activity and durability for methanol oxidation reaction has been one of the main focuses of researchers in recent years. Several works are reviewed in this paper to summarize and compare the performance of electrocatalysts comprising of noble and non-noble metals. The effect of manipulating catalysts by introducing nanostructured morphology, metal alloys, support materials, acidic or basic electrolyte, and synthesis methods are also examined. The paper finally concludes with details of challenges that are generally faced in making direct methanol fuel cell (DMFC) a reliable source of energy for future prospects, and the approach to be taken to reduce the complexity in synthesizing new generations of anode electrocatalysts.This publication was made possible by NPRP grant (NPRP8-145-2-066) from the Qatar National Research Fund (a member of Qatar foundation). The statements made herein are solely the responsibility of the author(s). The author(s) would also like to acknowledge the support from Qatar University internal grant QUCG-CENG-19/20-7. Open Access funding provided by the Qatar National Library.Scopu

Development of Co/Co9S8 metallic nanowire anchored on N-doped CNTs through the pyrolysis of melamine for overall water splitting

Herein, we report the successful synthesis of Co9S8 metal-sulfide nanowire trapped in multi walled carbon nanotube (MWCNT), which was subsequently found to be an effective catalyst for water splitting. Melamine pyrolysis together with a Co precursor results in MWCNTs, with the addition of sulfur during synthesis enhancing the surface area, pore size, and oxygen vacancy defects in the nanotubes. The hierarchical structure of Co/Co9S8/CNT products boosted the electron mobility and mass transport for both the oxygen evolution (OER) and hydrogen evolution reaction (HER) in alkaline medium. Doping the catalyst surface with Pyridinic-N atoms, Graphitic-N atoms and thioamide S-atoms dramatically improved the bifunctional electrocatalytic performance by lowering the overpotentials for OER and HER reactions. The Co/Co9S8/CNT generated a current density of 10 mAcm?2 water-splitting current by applying a cell voltage of only 1.5 V. Further, Co/Co9S8/CNT showed excellent stability. The mechanism of Co8S9 nanowire formation in the MWCNT was also investigated.This publication was made possible by NPRP Grant (NPRP8-145-2-066) from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the author(s). The authors also wish to gratefully acknowledge Centre of Advanced Materials (CAM) and Gas Processing Center (GPC) at Qatar University for XRD and XPS analysis respectively. The SEM analysis was accomplished in the Central Laboratories Unit, Qatar University. The authors would also like to acknowledge QEERI Core Labs for their support related to the TEM characterization. Open Access funding provided by the Qatar National Library. The raw data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study. The processed data required to reproduce these findings cannot be shared at this time as the data also forms part of an ongoing study. Anchu Ashok: Conceptualization, Methodology, Data curation, Formal analysis, Investigation, Validation, Writing - Original draft, Anand Kumar: Conceptualization, Supervision, Writing - Review & Editing, Project administration, Funding acquisition, Janarthanan Ponraj: Visualization, Investigation, Said A. Mansour: Visualization, InvestigationScopu

Synthesis and growth mechanism of bamboo like N-doped CNT/Graphene nanostructure incorporated with hybrid metal nanoparticles for overall water splitting

Herein, we report a melamine and metal-salt based pyrolysis technique for synthesizing metal encapsulated N-doped carbon nanotube (CNTs) in form of bamboo-like CNTs and multi walled CNTs (MWCNT). Sulfur doping during synthesis greatly influenced the physio-chemical properties of the material formed. X-ray diffraction (XRD) analysis confirms NiCo alloy (NiCo@CNT) formation that transformed into a hybrid NiCo/Co3Ni6S8/Co3O4 nanocomposite (NiCoS@CNT) in presence of sulfur. A detailed study was conducted on the mechanism of the formation of metal-encapsulated N-doped CNT structures from the polymerization of melamine. The unique NiCoS@CNT structure renders high specific surface area (232.2 m2/g), large pore volume (0.92 cm2/g), and high lattice defect with abundant oxygen vacancies resulting in excellent performance for OER and HER in alkaline medium. The hybrid catalyst requires over-potentials of 198 mV and 295 mV to deliver a current-density of 10 mAcm?2, respectively for HER and OER. A cell voltage of only 1.53 V was required to deliver a long-term stable current-density of 10 mAcm?2 for water splitting when NiCoS@CNT was used as both anode and cathode. Superior performance of NiCoS@CNT could be ascribed to high surface area, abundant active sites, fast charge-transfer rate, high pyridinic-N content and the presence of highly conductive CNT architecture.This publication was made possible by NPRP grant (NPRP8-145-2-066) from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the author(s). The authors also wish to gratefully acknowledge Centre of Advanced Materials (CAM) for XRD analysis and the SEM analysis was accomplished in the Central Laboratories Unit, Qatar University. The authors would also like to acknowledge QEERI Core Labs for their support related to the TEM characterization. Open Access funding provided by the Qatar National Library (QNL).Scopu

Preparation of Mesoporous/Microporous MnCo2O4 and Nanocubic MnCr2O4 Using a Single Step Solution Combustion Synthesis for Bifunction Oxygen Electrocatalysis

We report the synthesis of mesoporous/microporous MnCo2O4 and cubic MnCr2O4 using solution combustion synthesis for oxygen reduction and oxygen evolution reactions. XRD and TEM analysis indicate small crystallites of MnCo2O4 forming ultra-thin layer of irregular structures that lead to porous morphology. A slightly larger crystallite size was observed for MnCr2O4. The surface oxygen defect in MnCo2O4 is much higher than MnCr2O4 that enhances the active sites for the oxygen adsorption and promotes fast dissociation in presence of more exposed Mn/Co sites during the oxygen electrocatalysis. The electrochemical properties of the synthesized catalysts were analysed using CV, LSV, EIS and CA showing high limiting current density and kinetic current density, positive onset and halfwave potential and higher number of overall electron transfer in MnCo2O4 that MnCr2O4. Chronoamperometric (CA) runs for 24 h shows excellent stability of MnCo2O4 without any significant decrease in the current or potential value in ORR and OER. On basis of the activity and stability performance, MnCo2O4 shows to be a promising bifunctional electrocatalyst, with significantly improved performance than previously reported Mn and Co mixed oxides, and comparable to Pt and Ru based catalysts in terms of durability, onset potential and Tafel slope.Scopu

Recent advances in cobalt based heterogeneous catalysts for oxygen evolution reaction

The future of the world energy lies in clean and renewable energy sources. Many technologies, such as solar cells, wind turbines, etc., have been developed to harness renewable energies in different forms of fuel. Amongst them, electrolysis of water to produce oxygen and hydrogen is one of the paramount developments towards achieving clean energy, which has attained significant attention due to its green and simple method for the production of fuels. In electrolysis of water, the half-reaction containing the oxygen evolution reaction (OER) is a reaction that is kinetically sluggish, which requires higher overpotential to produce O2, when compared to the other half-reaction, i.e. hydrogen evolution reaction (HER). Many electrocatalysts are studied extensively to be used in the OER process to get an economical yield out of it. Noble metal-based catalysts are the state-of-the-art catalyst used for OER currently. But due to their high cost and scarcity, they cannot be applied in a large-scale manner to be used in the future. The non-noble metals (transition metals and perovskites) are gaining interest by exhibiting on par or better OER performance compared to the noble metal used. Due to their low cost, ample resources, and several metals available, they have opened up a variety of areas with a different combination of metals to be used as a catalyst for OER. Amongst these metals, cobalt has received massive appreciation for performing as an excellent OER catalyst. Multi metals, multimetal mixed oxides, multimetal phosphides, perovskites, and carbon-supported catalysts containing cobalt have shown low overpotential with high long-term stability. Therefore, in this review, we go through different cobalt-based electrocatalysts for OER, the general mechanism governing the OER process, the challenges that we are facing today to enhance the catalytic performance, and future aspects to overcome such challenges.This study was supported by the NPRP grant ( NPRP8-145-2-066 ) from the Qatar National Research Fund (a member of the Qatar Foundation). The statements made herein are solely the responsibility of the authors. The author(s) would also like to acknowledge the support from Qatar University 's internal grant QUCG-CENG-19/20-7 .Scopu

Electrocatalytic conversion of CO2 over in-situ grown Cu microstructures on Cu and Zn foils

Electrochemical conversion of carbon dioxide to value added multi-carbon products is of great importance and a promising approach to mitigate greenhouse gases. In this work, we report the fabrication of electrodes by depositing Cu over the metallic foils of Cu and Zn, which show high faradic efficiency for the conversion of CO2 to formic acid, acetate, and methanol. The morphology, phase and oxidation state of the Cu were different on the two foils while maintaining the same synthesis steps. The Cu particles embedded on Cu foil (Cu/Cu-foil) are in 3D cuboids form with flat and smooth faces, whereas Cu on Zn foil (Cu/Zn-foil) emerge in the shape of 3D flowers with the club of Cu microspikes grown perpendicularly from a root. For the electrocatalytic conversion of CO2, the Cu/Cu-foil shows a high selectivity for formic acid and ethyl acetate with the highest faradaic efficiency of 78 % at −0.3 V vs RHE, and 64 % at −1.0 V (vs RHE) for the two products, respectively. In contrast, the Cu/Zn-foil displays a high selectivity towards methanol, with the highest faradaic efficiency of 48 % at −1.0 V vs RHE, indicating that the product selectivity can be easily modulated by changing the metallic foil on which the Cu particles are deposited. Both the electrodes, Cu/Cu-foil and Cu/Zn-foil, show long-term stable performance while maintaining the selectivity of the products during CO2 electrocatalytic conversion

Single step synthesis of porous NiCoO2 for effective electrooxidation of glycerol in alkaline medium

Herein, we report the electrooxidation of glycerol in alkaline media in presence of highly active and durable NiCoO2 catalyst synthesized using single step solution combustion synthesis (SCS) and compare its activity with NiO and Co3O4 prepared using the same method. X-ray diffraction (XRD), X-Ray Photoelectron Spectroscopy (XPS), Scanning electron microscopy (SEM) with EDS and Transmission electron microscopy (TEM) along with EDS elemental/phase mapping were used to analyze the crystallinity, morphology and phase composition of the synthesized particles. TEM image with phase mapping confirms the existence of mixed NiCoO2 and these materials shows enhanced performance when compared with individual metal oxides. The onset potential of NiCoO2 is much lower and the oxidation current density obtained is relatively higher. More importantly, the current density and stability of NiCoO2 obtained from chronoamperometry makes it a promising catalyst for glycerol based fuel cells.This publication was made possible by NPRP grant (NPRP8-145-2-066) from the Qatar national research fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the author(s). The authors also wish to gratefully acknowledge the Gas Processing Centre (GPC) at Qatar University for carrying out the XRD and XPS measurements, the Central Laboratory Unit (CLU) for services related to electron microscopy. The author acknowledge Core Labs at the Qatar Environment and Energy Research Institute (QEERI) for their help in providing TEM and EDS analysis.Scopu

Ag/Co3O4 as an effective catalyst for glycerol electro-oxidation in alkaline medium

Herein, we report two different modes of combustion synthesis to prepare Ag/Co3O4 for glycerol electro-oxidation reaction. The synthesis technique allows us to deposit and disperse cobalt on the surface of silver and understand the effect of silver-cobalt interactions on the electrocatalytic performance. The bimetallic AgCo catalyst was synthesized via conventional solution combustion (AgCo-SCS); in addition, a novel second wave solution combustion synthesis (AgCo-SWC) was also used to synthesize a sample with a higher degree of surface alloying between the elements. XRD results of AgCo-SWC show peak shifts in 2? to indicate the formation of a solid solution alloy that could improve the structural and electronic characteristic of the material. In AgCo-SCS, smaller Ag particles are found to be more on the surface, while in AgCo-SWC, Ag particles were largely covered with cobalt particles. The electro-oxidation results indicate that AgCo-SWC has improved electrochemical properties in terms of higher oxidation current and lower onset potential, which makes it an ideal candidate for glycerol oxidation reaction.This publication was made possible by NPRP grant ( NPRP8-145-2-066 ) from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of the authors. We would like to thank the Gas Processing Centre for conducting XRD and XPS analysis. The SEM and TEM analysis were accomplished in the Central Laboratory Unit, Qatar University .Scopu