Platinum group metal-free (PGM-free) electrocatalysts for the oxygen reduction reaction (ORR) often exhibit a complex functionalized graphitic structure. Because of this complex structure, limited understanding exists about the design factors for the synthesis of high-performing materials. Graphene, a two-dimensional hexagonal structure of carbon, is amenable to structural and functional group modifications, making it an ideal analogue to study crucial properties of more complex graphitic materials utilized as electrocatalysts. In this paper, we report the synthesis of active nitrogen-doped graphene oxide catalysts for the ORR in which their activity and four-electron selectivity are enhanced using simple solvent and electrochemical treatments. The solvents, chosen based on Hansen’s solubility parameters, drive a substantial change in the morphology of the functionalized graphene materials by (i) forming microporous holes in the graphitic sheets that lead to edge defects and (ii) inducing 3D structure in the graphitic sheets that promotes ORR. Additionally, the cycling of these catalysts has highlighted the multiplicity of the active sites, with different durability, leading to a highly selective catalyst over time, with a minimal loss in performance. High ORR activity was demonstrated in an alkaline electrolyte with an onset potential of ∼1.1 V and half-wave potential of 0.84 V vs RHE. Furthermore, long-term stability potential cycling showed minimal loss in half-wave potential (<3%) in both N2- and O2-saturated solutions with improved selectivity toward the four-electron reduction after 10000 cycles. The results described in this work provide additional understanding about graphitic electrocatalysts in alkaline media that may be utilized to further enhance the performance of PGM-free ORR electrocatalysts.

Material interactions at the polymer electrolytes–catalyst interface play a significant role in the catalytic efficiency of alkaline anion-exchange membrane fuel cells (AEMFCs). In this work, the surface adsorption behaviors of the cation–hydroxide–water and phenyl groups of polymer electrolytes on Pd- and Pt-based catalysts are investigated using two Pd-based hydrogen oxidation catalystsPd/C and Pd/C-CeO2and two Pt-based catalystsPt/C and Pt-Ru/C. The rotating disk electrode study and complementary density functional theory calculations indicate that relatively low coadsorption of cation–hydroxide–water of the Pd-based catalysts enhances the hydrogen oxidation activity, yet substantial hydrogenation of the surface adsorbed phenyl groups reduces the hydrogen oxidation activity. The adsorption-driven interfacial behaviors of the Pd- and Pt-based catalysts correlate well with the AEMFC performance and short-term stability. This study gives insight into the potential use of non-Pt hydrogen oxidation reaction catalysts that have different surface adsorption characteristics in advanced AEMFCs.

Effect of organic cations on hydrogen oxidation reaction (HOR) of carbon supported platinum (Pt/C) is investigated using three 0.1 M alkaline electrolytes, tetramethylammonium hydroxide (TMAOH), tetrabutylammonium hydroxide (TBAOH) and tetrabutylphosphonium hydroxide (TBPOH). Rotating disk electrode experiments indicate that the HOR of Pt/C is adversely impacted by time-dependent and potential-driven chemisorption of organic cations. In-situ infrared reflection adsorption spectroscopy experiments indicated that the specific chemisorption of organic cations drives the hydroxide co-adsorption on Pt surface. The co-adsorption of TMA + and hydroxide at 0.1 V vs. reversible hydrogen electrode is the strongest; consequently, complete removal of the co-adsorbed layer from Pt surface is difficult even after exposure the Pt surface to 1.2 V. Conversely, the chemisorption of TBP + is the weakest, yet notable decrease of HOR current density is still observed. The adsorption energies, E, for TMA + , TBA + , and TBP + on Pt (111) surface from density functional theory are computed to be −2.79, −2.42 and −2.00 eV, respectively. The relatively low adsorption energy of TBP + is explained by the steric hindrance and electronic effect. This study emphasizes the importance of cationic group on HOR activity of alkaline anion exchange membrane fuel cells. Alkaline anion exchange membrane fuel cells (AAEMFCs) are drawing increasing interest due to the fact that non-precious group metal (non-PGM) catalysts perform well in alkaline environment. 1Over the last decade, numerous non-PGM catalysts have demonstrated excellent oxygen reduction reaction (ORR) activity.2,3 However, poor activity for the hydrogen oxidation reaction (HOR) is still a challenge under alkaline conditions even for Pt catalysts. Therefore, development of highly active HOR catalysts remain one of the major technical challenges, hampering the success of AAEMFCs. 4 The reason for the poor HOR activity in alkaline environments is unclear. Markovic et al. suggested that an optimal balance between the adsorption/dissociation of H 2 and the adsorption of hydroxyl species is critical for improving HOR activity.5 Conversely, Gasteiger et al. suggested that the hydrogen binding energy is the relevant descriptor for the HOR in alkaline electrolytes.6 Yan et al. further elucidated that the hydroxide species do not directly participate in the reaction through adsorption, while the alkalinity change induced by the hydroxide ion affects the hydrogen binding energy and in turn influences the HOR activity. 7While aforementioned studies primarily consider the fundamental Heyrovsky and Volmer steps to explain the slow HOR kinetics, recently Janik et al. have proposed that a co-adsorbed alkali metal cation-hydroxide-water layer on the Pt surface may impact the HOR activity as observed from density functional theory (DFT) calculations and electrochemical experiments.8 Substantial Pt HOR inhibition was observed with organic cation solutions, in addition to the alkali metal cation in aqueo...

Removal of intercalated water within graphitic sheets is critical to achieving high-performing oxygen reduction reaction catalysts.

The curing time, surface adhesion and water absorption characteristics of Sylgard 184 were modified through the addition of catalysts and fillers. Incorporation of small amounts of a platinum-based Karstedt catalyst greatly decreased curing time at room temperature, whereas the addition of talcum powder (talc), polytetrafluoroethylene (PTFE) and NaY zeolite fillers changed surface adhesion and functionality of Sylgard 184. Fourier-transform infrared spectroscopy (FT-IR), rheological and mechanical tests (tensile strength and hardness) were used to quantify the acceleration in the curing time. The surface adhesion was evaluated for aluminum and glass-like substrates using a 90° peel-off test. The interaction between fillers and Sylgard was studied by molecular dynamics simulations, which showed the interaction between NaY and Sylgard is This article is protected by copyright. All rights reserved. This is the author manuscript accepted for publication and has undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process, which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1002/app.48530 greater than that for PTFE. Water absorption studies indicated that 10 wt% NaY added to Sylgard 184 helped to improve water absorption, whereas incorporation of talc had the opposite effect.

State of the art proton exchange membrane fuel cells contain metallic cations as alloyed Pt catalysts or as additives to improve the chemical stability of membranes. While these novel materials have improved the performance and durability, they can leach out contaminants such as Ce, Ni and Co ions into the ionomer, impact the potency of the additive, decrease the ionomer conductivity and reduce fuel cell performance. We report here that in presence of Ce, Ni and Co, the ionomer conductivity (Nafion 211) decreases by a factor of ~3 with 5.2-19.2 mgmetal cm -3 at 80°C, 100% RH. This performance correlates with a decrease in ORR performance, most notably lower limiting currents 1.1x10 -1 mA cm -2 in proton form vs. 6.2-8.2x10 -2 mA cm 2 with 6-12 mgmetal cm -3 and lower ORR onset potentials at 25°C, 100% RH.

Glucose oxidase was immobilized by electropolymerization into films of polyaniline, polyindole, polypyrrole, poly(o‐phenylediamine), and polyaniline crosslinked with p‐phenylenediamine. The kinetics and the behavior of the entrapped enzyme toward elevated temperature, organic solvent denaturation, and pH were investigated, along with the response of the films to electroactive species such as acetaminophen, ascorbate, cysteine, and uric acid. For most of the films, linearity to glucose extended from 7 to 10 mM. The poly(o‐phenylenediamine)/glucose oxidase film gave the best signal/noise ratio and polypyrrole/glucose oxidase film gave the most reproducible current responses. No significant shift of the optimum reaction pH (5.5), except for polypyrrole (5.0), was observed after immobilization of glucose oxidase in the various films. Enzymatic activity decreased rapidly when pH was raised above 7.5. Thermodeactivation studies at 55°, 60°, and 65°C have shown polypyrrole/and poly(o‐phenylediamine)/glucose oxidase films to be the most resistant enzymatic films. Poly(o‐phenylenediamine) films offered the best protection against glucose oxidase deactivation in hexane, chloroform, ether, THF, and acetonitrile when compared with the other electropolymerized films. All the enzymatic films exhibited permselection toward electroactive species. © 1996 John Wiley & Sons, Inc.

Dimethyl ether (DME) is a promising alternative fuel option for direct‐feed low‐temperature fuel cells. Until recently, DME had not received the same attention as alcohol fuels, such as methanol or ethanol, despite its notable advantages. These advantages include a high theoretical open‐cell voltage (1.18 V at 25 °C) that is similar to that of methanol (1.21 V), much lower toxicity than methanol, and no need for the carbon−carbon bond scission that is needed in ethanol oxidation. DME is biodegradable, has a higher energy content than methanol (8.2 vs. 6.1 kWh kg−1), and, like methanol, can be synthesized from recycled carbon dioxide. Although the performance of direct DME fuel cells (DDMEFCs) has progressed over the past few years, DDMEFCs have not been viewed as fully viable. In this work, we report much improved performance from the ternary Pt55Ru35Pd10/C anode catalyst, allowing DDMEFCs to compete directly with direct methanol fuel cells (DMFCs). We also report results involving binary Pt alloys as reference catalysts and an in situ infrared electrochemical study to better understand the mechanism of DME electro‐oxidation on ternary PtRuPd/C catalysts.