Electrocatalytic oxidation of ethanol at Pd, Pt, Pd/Pt and Pt/Pd nano particles supported on poly 1,8-diaminonaphthalene film in alkaline medium

A hybrid FeOx/CoOx/Pt ternary nanocatalyst for augmented catalysis of formic acid electro-oxidation

Platinum-based catalysts that have long been used as the anodes for the formic acid electro-oxidation (FAO) in the direct formic acid fuel cells (DFAFCs) were susceptible to retrogradation in performance due to CO poisoning that impaired the technology transfer in industry. This work is designed to overcome this challenge by amending the Pt surface sequentially with nanosized cobalt (nano-CoOx, fibril texture of ca. 200 nm in particle size) and iron (nano-FeOx, nanorods of particle size and length of 80 and 253 nm, respectively) oxides. This enriched the Pt surface with oxygenated groups that boosted FAO and mitigated the CO poisoning. The unfilled d-orbitals of the transition metals and their tendency to vary their oxidations states presumed their participation in a faster mechanism of FAO. Engineering the Pt surface in this FeOx/CoOx/Pt hierarchy resulted in a remarkable activity toward FAO, that exceeded four times that of the Pt catalyst with up to ca. 2.5 times improvement in the catalytic tolerance against CO poisoning. This associated a ca. - 32 mV shift in the onset potential of FAO which increased to - 40 mV with a post-activation of the same catalyst at - 0.5  in 0.2 mol L-1 NaOH, displaying the catalyst's competitiveness in reducing overpotentials in DFAFCs. It also exhibited a favorable amelioration in the catalytic durability in long-termed chronoamperometric electrolysis. The electrochemical impedance spectroscopy and the CO stripping voltammetry were employed to elucidate the origin of enhancement.

Interface Engineering of PdPt Ultrafine Ethanol Electro-Oxidation Nanocatalysts by Bacterial Soluble Extracellular Polymeric Substances (s-EPS) to Break through Sabatier Principle

Unsatisfactory performance of ethanol oxidation reaction (EOR) catalysts hinders the application of direct ethanol fuel cells (DEFCs), while traditional alloy catalysts (like PdPt) is cursed by Sabatier principle due to countable active site types. However, bacterial soluble extracellular polymeric substances (s-EPS) owning abundent functional groups may help breacking through it by contrusting different active sites on PdPt and inducing them to play synergy effect, which is called interface engineering. Using s-EPS to engineer catalysts is more green and consumes lower energy compared to chemical reagents. Herein, PdPt alloy nanoparticles (≈2.1 nm) are successfully in situ synthesized by/on s-EPS of Bacillus megaterium, an ex-holotype. Tryptophan residuals are proved as the main reductant. In EOR, PdPt@s-EPS shows higher activity (3.89 mA cm-2) than Pd@s-EPS, Pt@s-EPS, Pt/C and most reported akin catalysts. Its stability and durability are excellent, too. DFT modelling further demonstrates that, interface engineering by s-EPS breaks through Sabatier principle, by the synergy of diverse sites owning different degrees of d-p orbital hybridization. This work not only makes DEFCs closer to practice, but provides a facile and green strategy to design more catalysts.

Interfacial Electronic Interactions within the Pd-CeO2/Carbon Onions Define the Efficient Electrocatalytic Ethanol Oxidation Reaction in Alkaline Electrolytes

Porous Pd-based electrocatalysts are promising materials for alkaline direct ethanol fuel cells (ADEFCs) and ethanol sensors in the development of renewable energy and point-of-contact ethanol sensor test kits for drunk drivers. However, experimental and theoretical investigations of the interfacial interaction among Pd nanocrystals on supports (i.e., carbon black (CB), onion-like carbon (OLC), and CeO2/OLC) toward ADEFC and ethanol sensors are not yet reported. This is based on the preparation of Pd-CeO2/OLC nanocrystals by the sol-gel and impregnation methods. Evidently, the porous Pd-CeO2/OLC significantly increased membrane-free micro-3D-printed ADEFC performance with a high peak power density (Pmax = 27.15 mW cm-2) that is 1.38- and 7.58-times those of Pd/OLC (19.72 mW cm-2) and Pd/CB (3.59 mW cm-2), besides its excellent stability for 48 h. This is due to the excellent interfacial interaction among Pd, CeO2, and OLC, evidenced by density functional theory (DFT) simulations that showed a modulated Pd d-band center and facile active oxygenated species formation by the CeO2 needed for ethanol fuel cells. Similarly, Pd-CeO2/OLC gives excellent sensitivity (0.00024 mA mM-1) and limit of detection (LoD = 8.7 mM) for ethanol sensing and satisfactory recoveries (89-108%) in commercial alcoholic beverages (i.e., human serum, Amstel beer, and Nederberg Wine). This study shows the excellent possibility of utilizing Pd-CeO2/OLC for future applications in fuel cells and alcohol sensors.

The Effect of a Hydrogen Reduction Procedure on the Microbial Synthesis of a Nano-Pd Electrocatalyst for an Oxygen-Reduction Reaction

Noble-metal electrocatalysts supported by biological-organism-derived carbons have attracted attention from the public due to the growing demands for green synthesis and environmental protection. Carbonization at high temperatures and hydrogen reduction are critical steps in this technical route. Herein, Shewanella oneidensis MR-1 were used as precursors, and the effects of the hydrogen-reduction procedure on catalysts were explored. The results showed that the performances of FHTG (carbonization followed by hydrogen reduction) displayed the best performance. Its ECSA (electrochemical surface area), MA (mass activity), and SA (specific activity) reached 35.01 m2 g−1, 58.39 A·g−1, and 1.66 A cm−2, respectively, which were 1.17, 1.75, and 1.50 times that of PHTG (prepared through hydrogen reduction followed by carbonization) and 1.56, 2.26, and 1.44 times that of DHTG (double hydrogen reduction). The high performance could be attributed to its fine particle size and rich N content, and the specific regulation mechanism was also proposed in this paper. This study opens a practical guide for effectively avoiding particle agglomeration during the fabrication process for catalysts.

Acetonitrile’s Effect on the Efficiency of Ethanol Electrooxidation at a Polycrystalline Pt Electrode in Relation to pH-Dependent Fuel Cell Applications

The present paper reports cyclic voltammetric and a.c. impedance spectroscopy investigations on the influence of the acetonitrile concentration on the kinetics (and individual product’s efficiency) of the ethanol oxidation reaction (EOR), performed on a polycrystalline Pt electrode surface in 0.5 M H2SO4 and 0.1 M NaOH supporting solutions. The kinetics of the EOR were examined at room temperature over the voltammetric potential range, which covers the electrooxidation of surface-adsorbed COAds species, as well as the formation of acetaldehyde molecules. In addition, the time-dependent efficiency of acetate and acetaldehyde formation in relation to the initial acetonitrile content for both acidic and alkaline electrolytes was evaluated by means of spectrophotometric Ultraviolet/ Visible Spectroscopy (UV-VIS) instrumental analysis.

Ethanol Electrooxidation at Platinum-Rare Earth (RE = Ce, Sm, Ho, Dy) Binary Alloys

Proton exchange membrane fuel cells and direct alcohol fuel cells have been extensively studied over the last three decades or so. They have emerged as potential systems to power portable applications, providing clean energy, and offering good commercial viability. Ethanol is considered one of the most interesting fuels in this field. Herein, platinum-rare earth (Pt-RE) binary alloys (RE = Ce, Sm, Ho, Dy, nominal composition 50 at.% Pt) were produced and studied as anodes for ethanol oxidation reaction (EOR) in alkaline medium. A Pt-Dy alloy with nominal composition 40 at.% Pt was also tested. Their electrocatalytic performance was evaluated by voltammetric and chronoamperometric measurements in 2 M NaOH solution with different ethanol concentrations (0.2–0.8 M) in the 25–45 °C temperature range. Several EOR kinetic parameters were determined for the Pt-RE alloys, namely the charge transfer and diffusion coefficients, and the number of exchanged electrons. Charge transfer coefficients ranging from 0.60 to 0.69 and n values as high as 0.7 were obtained for the Pt0.5Sm0.5 electrode. The EOR reaction order at the Pt-RE alloys was found to vary between 0.4 and 0.9. The Pt-RE electrodes displayed superior performance for EOR than bare Pt, with Pt0.5Sm0.5 exhibiting the highest electrocatalytic activity. The improved electrocatalytic activity in all of the evaluated Pt-RE binary alloys suggests a strategy for the solution of the existing anode issues due to the structure-sensitive EOR.

Mono and dual hetero-structured M@poly-1,2 diaminoanthraquinone (M = Pt, Pd and Pt–Pd) catalysts for the electrooxidation of small organic fuels in alkaline medium

Oxidation of some small organic fuels such as methanol (MeOH), ethanol (EtOH) and ethylene glycol (EG) was carried out in an alkaline medium using palladium (Pd)–platinum (Pt) nanoparticles/poly1,2-diaminoanthraquinone/glassy carbon (p1,2-DAAQ/GC) catalyst electrodes. Pd and Pt were incorporated into the p1,2-DAAQ/GC electrode using the cyclic voltammetry (CV) technique. The obtained Pd/p1,2-DAAQ/GC, Pt/p1,2-DAAQ/GC, Pt/Pd/p1,2-DAAQ/GC and Pd/Pt/p1,2-DAAQ/GC nanocatalyst electrodes were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and CV methods. Real active surface area (A_real) achieved by carbon monoxide (CO) adsorption using differential electrochemical mass spectroscopy (DEMS) technique. The electrochemical activity was evaluated and normalized to A_real per metal loading mass. The electrocatalytic oxidation of the small organic fuels at the prepared nanocatalyst electrodes was studied in 1.0 M NaOH solutions by CV and chronoamperometric (CA) techniques. Pt/Pd/p1,2-DAAQ/GC nanocatalyst electrode exhibited enhanced catalytic activity, better durability and higher tolerance to carbon monoxide generated in the oxidation reaction when compared with the other three studied nanocatalysts. The present investigation suggests that the studied nanocatalysts can be successfully applied in direct oxidation of small organic fuels, especially MeOH.

Oxidation reaction of some small organic fuels such as methanol, ethanol and ethylene glycol was carried out in alkaline medium at palladium (Pd)–platinum (Pt) nanoparticles/poly1,2-diaminoanthraquinone/glassy carbon catalyst electrodes.

Synthesis and facile structure-adjusting of Pd–Pt nanocrystal electrocatalysts with improved activity for ethanol oxidation reaction

Illustration of the synthesis of the nanospheroid-, nanoflower- and nanoworm-Pd–Pt NCs and their electrocatalytic activity for ethanol oxidation.