Alkaline Ethanol Oxidation Reaction on Carbon Supported Ternary PdNiBi Nanocatalyst using Modified Instant Reduction Synthesis Method

High performance chitosan/nanocellulose-based composite membrane for alkaline direct ethanol fuel cells

Polysaccharide anion exchange membranes (AEMs) containing chitosan (CS), cellulose nanofibrils (CNFs) and CNFs quaternized with poly(diallyldimethylammonium chloride) (CNF(P)s) were developed for use in alkaline direct ethanol fuel cells (ADEFCs). The resulting composite membranes prepared by the solvent casting process based on an experimental design were comprehensively assessed for morphology, KOH uptake, swelling ratio, EtOH permeability, mechanical properties, ionic conductivity, and cell performance. The fabricated CS-based composite membranes with CNF(P) fillers were superior to the commercial Fumatech FAA-3-50 membrane in terms of Young's modulus and tensile strength (69 % and 85 % higher, respectively), ion exchange capacity (169 % higher), and ionic conductivity (228 % higher). Single fuel cell tests have shown excellent performance of the CS-based membranes with CNF and CNF(P) fillers, as they exhibited up to 86 % improvement in power density at 80 °C compared to the commercial membrane (65.1 mW/cm2 vs. 35.1 mW/cm2) and higher maximum power density at all test conditions.

Enhanced Nitrogen Reduction to Ammonia by Surface- and Defect-Engineered Co-catalyst-Modified Perovskite Catalysts under Ambient Conditions and Their Charge Carrier Dynamics

An electrocatalytic nitrogen reduction reaction is considered a potential approach for green ammonia production─a zero-carbon fertilizer, fuel, and energy storage for renewable energy. To harness the synergistic properties of perovskites, the inherent dipole moment due to their non-centrosymmetric structure (that facilitates better charge separation), oxygen vacancies, and the presence of Ni metal sites that permit activation and reduction of N₂ efficiently, the NiTiO₃-based nanoelectrocatalysts have been synthesized. Further, these catalysts have been modified with ultra-small metal nanocrystal co-catalysts to form heterointerfaces that not only aid to improve the charge separation but also activate N₂ and lower overpotential requirements. The appearance of peaks corresponding to (012), (104), (110), (11-3), (024), (11-6), (018), (027), and (300) confirms the formation of rhombohedral NiTiO_3. The shift in the XRD peak corresponding to the (104) plane to a smaller 2θ value and peak shifting and widening of Raman spectra imply the lattice distortion that signifies the formation of Pd-NiTiO₃ and Pt-NiTiO₃ heterojunction electrocatalysts with the loadings of 0.4 and 0.3 wt % of Pd and Pt, respectively, as confirmed by ICP-OES analysis. The detailed XPS analysis reveals the presence of Pd (0), Pd (II), and Pt (0), Pt (II) in respective electrocatalysts. The appearance of XPS peaks at 528.7 and 531.1 eV suggests the presence of oxidative oxygen species (O^2-/O^-) and the presence of oxygen defects due to oxygen vacancy. The detailed nitrogen reduction (NRR) investigation exhibits a 5-fold enhancement in ammonia yield rate (∼14.28 μg h^-1 mg^-1 at -0.003 V vs RHE), a faradic efficiency of 27% (at 0.097 V vs RHE) for Pd-NiTiO₃ electrocatalysts than that for bare NiTiO₃ (3.08 μg h^-1 mg^-1), and 9-folds higher than that of the activity shown by the commercial TiO₂ (P₂₅) (1.52 μg h^-1mg^-1). The formation of ammonia was further confirmed by using isotopic nitrogen as the feeding gas. Furthermore, the highest NRR is observed at lower cathodic potential (-0.003 V vs RHE) in the case of the Pd-NiTiO₃ electrocatalyst than that of the Pt-NiTiO₃ electrocatalyst (-0.203 V vs RHE), implying significantly reduced overpotential requirement. Such enhanced NRR activity with lower overpotential requirement in the case of the Pd-NiTiO₃ electrocatalyst is due to efficient charge separation as shown by the semicircle Nyquist plot, decreased photoluminescence emission intensity, shorter average lifetime (∼29 ns) of excitons, appropriate band bending, and improved activation of N₂ by the oxygen vacancies and heterointerface formed between Pd nanocrystals and NiTiO₃. Furthermore, no change is observed in the current density, after stabilization in the initial few seconds, even up to 2 h, which signifies that these electrocatalysts are stable. The structural and morphological integrity of the optimized catalyst remained even after the nitrogen reduction reactions, as revealed by no significant change observed in FESEM, elemental mapping, and EDS analysis.

Efficiency of Neat and Quaternized-Cellulose Nanofibril Fillers in Chitosan Membranes for Direct Ethanol Fuel Cells

In this work, fully polysaccharide based membranes were presented as self-standing, solid polyelectrolytes for application in anion exchange membrane fuel cells (AEMFCs). For this purpose, cellulose nanofibrils (CNFs) were modified successfully with an organosilane reagent, resulting in quaternized CNFs (CNF (D)), as shown by Fourier Transform Infrared Spectroscopy (FTIR), Carbon-13 (C13) nuclear magnetic resonance (¹³C NMR), Thermogravimetric Analysis (TGA)/Differential Scanning Calorimetry (DSC), and ζ-potential measurements. Both the neat (CNF) and CNF(D) particles were incorporated in situ into the chitosan (CS) membrane during the solvent casting process, resulting in composite membranes that were studied extensively for morphology, potassium hydroxide (KOH) uptake and swelling ratio, ethanol (EtOH) permeability, mechanical properties, ionic conductivity, and cell performance. The results showed higher Young's modulus (119%), tensile strength (91%), ion exchange capacity (177%), and ionic conductivity (33%) of the CS-based membranes compared to the commercial Fumatech membrane. The addition of CNF filler improved the thermal stability of the CS membranes and reduced the overall mass loss. The CNF (D) filler provided the lowest (4.23 × 10^-5 cm² s^-1) EtOH permeability of the respective membrane, which is in the same range as that of the commercial membrane (3.47 × 10^-5 cm²s^-1). The most significant improvement (~78%) in power density at 80 °C was observed for the CS membrane with neat CNF compared to the commercial Fumatech membrane (62.4 mW cm^-2 vs. 35.1 mW cm^-2). Fuel cell tests showed that all CS-based anion exchange membranes (AEMs) exhibited higher maximum power densities than the commercial AEMs at 25 °C and 60 °C with humidified or non-humidified oxygen, demonstrating their potential for low-temperature direct ethanol fuel cell (DEFC) applications.

Influence of the electrocatalyst layer thickness on alkaline DEFC performance

Determining the optimum layer thickness, for the anode and cathode, is of utmost importance for minimizing the costs of the alkaline direct ethanol fuel cell (DEFC) without lowering the electrochemical performance. In this study, the influence of layer thickness on the performance of the ethanol oxidation reaction (EOR) and oxygen reduction reaction (ORR) in an alkaline medium and resistance was investigated. The prepared gas diffusion electrodes (GDEs) were fully characterized, with scanning electron microscopy to determine the layer thickness and electrochemically in half-cell configuration. Cyclic voltammetry and polarization curve measurements were used to determine the oxidation and reduction processes of the metals, the electrochemical active surface area, and the activity towards the ORR and EOR. It was demonstrated that realistic reaction conditions can be achieved with simple and fast half-cell GDE measurements. Single cell measurements were conducted to evaluate the influence of factors, such as membrane or ethanol crossover. In addition, electrochemical impedance spectra investigation was performed to identify the effect of layer thickness on resistance. This successfully demonstrated that the optimal layer thicknesses and high maximum power density values (120 mW cm^-2) were achieved with the Pt-free catalysts and membranes used.

Mechanistic effects of blending formic acid with ethanol on Pd activity towards formic acid oxidation in acidic media

The direct formic acid fuel cell (DFAFC) is one of the most promising direct liquid fuel cells. Pd is the most active catalyst towards formic oxidation, however, it suffers from CO-like poisoning and instability in acidic media. Blending formic acid with ethanol is known to synergistically enhance the Pt catalytic activity of Pt. However, it has not been studied in the case of Pd. In this study, ethanol/formic acid blends were tested, aiming at understanding the effect of ethanol on the formic acid oxidation mechanism at Pd and how the direct and indirect pathways could be affected. The blends consisted of different formic acid (up to 4 M) and ethanol (up to 0.5 M) concentrations. The catalytic activity of a 40% Pd/C catalyst was tested in 0.1 M H2SO4 + XFA + YEtOH using cyclic voltammetry, while the catalyst resistance to poisoning in the presence and absence of ethanol was tested using chronopotentiometry. The use of these blends is found to not only eliminate the indirect pathway but also slowly decrease the direct pathway activity too. That is believed to be due to the different ethanol adsorption orientations at different potentials. This study should open the door for further studying the oxidation of FA/ethanol blends using different pHs and different Pd-based catalysts.

A comprehensive and critical review of the recent progress in electrocatalysts for the ethanol oxidation reaction

The human craving for energy is continually mounting and becoming progressively difficult to gratify. At present, the world's massive energy demands are chiefly encountered by nonrenewable and benign fossil fuels. However, the development of dynamic energy cradles for a gradually thriving world to lessen fossil fuel reserve depletion and environmental concerns is currently a persistent issue for society. The discovery of copious nonconventional resources to fill the gap between energy requirements and supply is the extreme obligation of the modern era. A new emergent, clean, and robust alternative to fossil fuels is the fuel cell. Among the different types of fuel cells, the direct ethanol fuel cell (DEFCs) is an outstanding option for light-duty vehicles and portable devices. A critical tactic for obtaining sustainable energy sources is the production of highly proficient, economical and green catalysts for energy storage and conversion devices. To date, a broad range of research is available for using Pt and modified Pt-based electrocatalysts to augment the C2H5OH oxidation process. Pt-based nanocubes, nanorods, nanoflowers, and the hybrids of Pt with metal oxides such as Fe2O3, TiO2, SnO2, MnO, Cu2O, and ZnO, and with conducting polymers are extensively utilized in both acidic and basic media. Moreover, Pd-based materials, transition metal-based materials, as well as transition metal-based materials are also points of interest for researchers nowadays. This review article delivers a broad vision of the current progress of the EOR process concerning noble metals and transition metals-based materials.

Well-defined polyindole–Au NPs nanobrush as a platform for electrochemical oxidation of ethanol

Over the recent decades, conducting polymers have received great interest in many fields including microelectronics, energy conversion devices, and biosensing due to their unique properties like electrical conductivity, stability, and simple synthesis. Modification of conducting polymers with noble metals e.g. gold enhances their properties and opens new opportunities to also apply them in other fields like electrocatalysis. Here, we focus on the synthesis of hybrid material based on polyindole (PIN) nanobrush modified with gold nanoparticles and its application towards electrooxidation of ethanol. The paper presents systematic studies from synthesis to electrochemical sensing applications. For the characterization of PIN–Au composites, scanning electron microscopy and X-ray diffraction analyses were used. The electrocatalytic performance of the proposed hybrid material towards alcohol oxidation was studied in alkaline media by cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy techniques. The results show that PIN–Au hybrid can be employed as an effective and sensitive platform for the detection of alcohols, which makes it a promising material in electrocatalysis or sensors. Moreover, the proposed composite exhibits electrocatalytic activity towards ethanol oxidation, which combined with its good long-term stability opens the opportunity for its application in fuel cells.

Efficient Chitosan/Nitrogen-Doped Reduced Graphene Oxide Composite Membranes for Direct Alkaline Ethanol Fuel Cells

Herein, we prepared a series of nanocomposite membranes based on chitosan (CS) and three compositionally and structurally different N-doped graphene derivatives. Two-dimensional (2D) and quasi 1D N-doped reduced graphene oxides (N-rGO) and nanoribbons (N-rGONRs), as well as 3D porous N-doped graphitic polyenaminone particles (N-pEAO), were synthesized and characterized fully to confirm their graphitic structure, morphology, and nitrogen (pyridinic, pyrrolic, and quaternary or graphitic) group contents. The largest (0.07%) loading of N-doped graphene derivatives impacted the morphology of the CS membrane significantly, reducing the crystallinity, tensile properties, and the KOH uptake, and increasing (by almost 10-fold) the ethanol permeability. Within direct alkaline ethanol test cells, it was found that CS/N rGONRs (0.07 %) membrane (Pmax. = 3.7 mWcm-2) outperformed the pristine CS membrane significantly (Pmax. = 2.2 mWcm-2), suggesting the potential of the newly proposed membranes for application in direct ethanol fuel cells.