Elod Gyenge

Electrocatalysis of borohydride oxidation: a review of density functional theory approach combined with experimental validation

The electrocatalysis of borohydride oxidation is a complex, up-to-eight-electron transfer process, which is essential for development of efficient direct borohydride fuel cells. Here we review the progress achieved by density functional theory (DFT) calculations in explaining the adsorption of BH4(-) on various catalyst surfaces, with implications for electrocatalyst screening and selection. Wherever possible, we correlate the theoretical predictions with experimental findings, in order to validate the proposed models and to identify potential directions for further advancements.

Borohydride-tolerant oxygen electroreduction catalyst for mixed-reactant Swiss-roll direct borohydride fuel cells

A novel and highly active Fe–aminoantipyrine (Fe–AAPyr) catalyst for oxygen reduction reaction (ORR) in alkaline media was synthesized by the modified sacrificial support method (SSM) and investigated in an innovative Swiss-roll mixed-reactant alkaline fuel cell architecture. The prepared Fe–AAPyr cathode showed excellent shorter-term (up to 200 min) durability and tolerance to electrooxidation of NaBH4. The Swiss-roll mixed-reactant Direct Borohydride Fuel Cell (DBFC) equipped with a Pt 3D anode and Fe–AAPyr gas-diffusion cathode produced an open circuit voltage and peak power density of 0.97 V and 137 mW cm−2 respectively at 45 °C and ambient pressure. These values are among the highest open circuit voltages and peak power densities reported for any mixed-reactant low temperature fuel cell and conventional dual chamber DBFCs.

Physicochemical Properties of Alkaline Aqueous Sodium Metaborate Solutions

Background: The transition to a hydrogen fuel economy is hindered by the lack of a practical storage method and concerns associated with its safe handling. Chemical hydrides have the potential to address these concerns. Sodium borohydride (sodium tetrahydroborate, NaBH 4 ), is the most attractive chemical hydride for H 2 generation and storage in automotive fuel cell applications, but recycling from sodium metaborate (NaBO 2 ), is difficult and costly. An electrochemical regeneration process could represent an economically feasible and environmentally friendly solution. Method of Approach: We report a study of the properties of concentrated NaBO 2 alkaline aqueous solutions that are necessary to the development of electrochemical recycling methods. The solubility, pH, density, conductivity, and viscosity of aqueous NaBO 2 solutions containing varying weight percentages (1, 2, 3, 5, 7.5, and 10 wt. %) of alkali hydroxides (NaOH, KOH, and LiOH) were evaluated at 25 ° C. The precipitates formed in supersaturated solutions were characterized by X-ray diffraction and scanning electron microscopy. Results: All NaBO 2 physicochemical properties investigated, except solubility, increased with increased hydroxide ion concentration. The solubility of NaBO 2 was enhanced by the addition of KOH to the saturated solution, but decreased when LiOH and NaOH were used. The highest ionic conductivity (198.27 S/m) was obtained from the filtrate of saturated aqueous solutions containing more than 30 wt. % NaBO 2 and 10 wt. % NaOH prior to filtration. At 10 wt. % hydroxide, the viscosity of the NaBO 2 solution was the highest in the case of LiOH (11.38 cP) and lowest for those containing NaOH (6.37 cP). The precipitate was hydrated, NaBO 2 for all hydroxides, but its hydration level was unclear. Conclusions: The use of KOH as the electrolyte was found to be more advantageous for the H 2 storage and generation system based on NaBO 2 solubility and solution half-life. However, the addition of NaOH led to the highest ionic conductivity, and its use seems more suitable for the electroreduction of NaBO 2 . Further investigations on the impact of KOH and NaOH on the electroreduction of NaBO 2 in aqueous media have the potential to enhance the commercial viability of NaBH 4 .

Controlling the Interfacial Environment in the Electrosynthesis of MnOx Nanostructures for High-Performance Oxygen Reduction/Evolution Electrocatalysis

High-performance, nonprecious metal bifunctional electrocatalysts for the oxygen reduction and evolution reactions (ORR and OER, respectively) are of great importance for rechargeable metal-air batteries and regenerative fuel cells. A comprehensive study based on statistical design of experiments is presented to investigate and optimize the surfactant-assisted structure and the resultant bifunctional ORR/OER activity of anodically deposited manganese oxide (MnOx) catalysts. Three classes of surfactants are studied: anionic (sodium dodecyl sulfate, SDS), non-ionic (t-octylphenoxypolyethoxyethanol, Triton X-100), and cationic (cetyltrimethylammonium bromide, CTAB). The adsorption of surfactants has two main effects: increased deposition current density due to higher Mn2+ and Mn3+ concentrations at the outer Helmholtz plane (Frumkin effect on the electrodeposition kinetics) and templating of the MnOx nanostructure. CTAB produces MnOx with nanoneedle (1D) morphology, whereas nanospherical- and nanopetal-like morphologies are obtained with SDS and Triton, respectively. The bifunctional performance is assessed based on three criteria: OER/ORR onset potential window (defined at 2 and -2 mA cm-2) and separately the ORR and OER mass activities. The best compromise among these three criteria is obtained either with Triton X-100 deposited catalyst composed of MnOOH and Mn3O4 or SDS deposited catalyst containing a combination of α- and β-MnO2, MnOOH, and Mn3O4.The interaction effects among the deposition variables (surfactant type and concentration, anode potential, Mn2+ concentration, and temperature) reveal the optimal strategy for high-activity bifunctional MnOx catalyst synthesis. Mass activities for OER and ORR up to 49 A g-1 (at 1556 mVRHE) and -1.36 A g-1 (at 656 mVRHE) are obtained, respectively.

Physicochemical Transport Properties of Aqueous Sodium Metaborate Solutions for Sodium Borohydride Hydrogen Generation and Storage and Fuel Cell Applications

The conductivity and viscosity of aqueous solutions of NaBO2 were measured as a function of concentration at 25oC. Conductivity data was analyzed with various Kohlrausch correlations and the limiting molar conductivity of the BO2 - ion at infinite dilution was estimated to be of 30.59 S.cm2/mol. From this value, the mobility, diffusion coefficients and transference number for the BO2 - ion were calculated as 3.17x10-4 cm2/s.V, 8.14x10-6 cm2/s, and 0.379 respectively. Ion-solvent and ion-ion interactions were studied with Jones-Dole type correlations, which were employed to analyze the viscosity data. A value of -0.4660 1/M was estimated for the BO2 - B- coefficient.

Surfactant Assisted Catalyst Layer Deposition for PEM Fuel Cells

Fuel Cells A. Bauer, D. P. Wilkinson, E. L. Gyenge, D. Bizzotto and S. Ye 1 Department of Chemical and Biological Engineering The University of British Columbia 2360 East Mall, Vancouver, BC, Canada, V6T 1Z3 2 Department of Chemistry, Advanced Materials Process and Engineering Laboratory The University of British Columbia 2355 East Mall Vancouver, BC, Canada, V6T 1Z4 3 Ballard Power Systems, 9000 Glenlyon Parkway, Burnaby, BC, Canada, V5J 5J8