Elucidation of role of graphene in catalytic designs for electroreduction of oxygen

Graphene is, in principle, a promising material for consideration as component (support, active site) of electrocatalytic materials, particularly with respect to reduction of oxygen, an electrode reaction of importance to low-temperature fuel cell technology. Different concepts of utilization, including nanostructuring, doping, admixing, preconditioning, modification or functionalization of various graphene-based systems for catalytic electroreduction of oxygen are elucidated, as well as important strategies to enhance the systems' overall activity and stability are discussed

Evaluation of Reduced-Graphene-Oxide Aligned with WO3-Nanorods as Support for Pt Nanoparticles during Oxygen Electroreduction in Acid Medium

Hybrid supports composed of chemically-reduced graphene-oxide-aligned with tungsten oxide nanowires are considered here as active carriers for dispersed platinum with an ultimate goal of producing improved catalysts for electroreduction of oxygen in acid medium. Here WO3 nanostructures are expected to be attached mainly to the edges of graphene thus making the hybrid structure not only highly porous but also capable of preventing graphene stacking and creating numerous sites for the deposition of Pt nanoparticles. Comparison has been made to the analogous systems utilizing neither reduced graphene oxide nor tungsten oxide component. By over-coating the reduced-graphene-oxide support with WO3 nanorods, the electrocatalytic activity of the system toward the reduction of oxygen in acid medium has been enhanced even at the low Pt loading of 30 microg cm-2. The RRDE data are consistent with decreased formation of hydrogen peroxide in the presence of WO3. Among important issues are such features of the oxide as porosity, large population of hydroxyl groups, high Broensted acidity, as well as fast electron transfers coupled to unimpeded proton displacements. The conclusions are supported with mechanistic and kinetic studies involving double-potential-step chronocoulometry as an alternative diagnostic tool to rotating ring-disk voltammetry.Comment: arXiv admin note: text overlap with arXiv:1805.0315

Optimization of carbon-supported platinum cathode catalysts for DMFC operation.

In this paper, we describe performance and optimization of carbon-supported cathode catalysts at low platinum loading. We find that at a loading below 0.6 mg cm-2 carbon-supported platinum outperforms platinum black as a DMFC cathode catalyst. A catalyst with a 1:1 volume ratio of the dry NafionTM to the electronically conducting phase (platinum plus carbon support) provides the best performance in oxygen reduction reaction. Thanks to improved catalyst utilization, carbon-supported catalysts with a platinum content varying from 40 wt% to 80 wt% deliver very good DMFC performance, even at relatively modest precious metal loadings investigated in this work

ADVANCES IN DIRECT METHANOL FUEL CELL SCIENCE& TECHNOLOGY AT LOS ALAMOS NATIONAL LABORATORY

. This paper describes recent advances in work on direct methanol fuel cells (DMFCS) at Los Alamos National Laboratory (LANL). The effort on DMFCS at LANL includes work on potential portable power applications, supported by the Defense Advanced Research Project Agency (DARPA), and work on potential transportation applications, supported by the US DOE. We describe results obtained with DMFC stack hardware of cell width limited to 2 mm, that allows operation with low air flow and at low air pressure drops. A 30-cell stack of 45-cm2 active area has been fabricated and tested. Power densities of 300 Wfl and 1 kWZ (of active stack volume) seem achievable under conditions applicable to portable power and transportation application, respectively. DMFCS with significantly lower catalyst loadlngs have been demonstrated showing maximum power density loss of only 20-30% as the catalyst loading is lowered by an order of magnitude. A 100 mW air breathing DMFC has been fabricated and tested demonstrating 3000 hours of continuous operation. Such air breathing DMFCS are behg further developed for applications in consumer electronics

Direct Methanol Fuel Cells at Reduced Catalyst Loadings

We focus in this paper on the reduction of catalyst loading in direct methanol fuel cells currently under development at Los Alamos National Laboratory. Based on single-cell DMFC testing, we discuss performance vs. catalyst loading trade-offs and demonstrate optimization of the anode performance. We also show test data for a short five-cell DMFC stack with the average total platinum loading of 0.53 mg cm{sup {minus}2} and compare performance of this stack with the performance of a single direct methanol fuel cell using similar total amount of precious metal

2,2’-Dipyridylamine as Heterogeneous Organic Molecular Electrocatalyst for Two-Electron Oxygen Reduction Reaction in Acid Media

Continuous production of hydrogen peroxide (H2O2) through the two-electron oxygen reduction reaction (2e-ORR) in distributed electrochemical cells offers important advantages for point-of-use water treatment and pulp bleaching over the complex industrial anthraquinone process. A low-cost, heterogeneous 2e-ORR electrocatalyst with high activity and selectivity is key to meeting the future needs for distributed production of H2O2 with large capacity. Herein, we demonstrate high activity and selectivity of a new heterogeneous organic molecular electrocatalyst, 2,2’-dipyridylamine, with an H2O2 yield of ca. 80%, and an onset potential of ca. 0.60 V vs. RHE in acidic aqueous electrolyte. We show that this acid-compatible, inexpensive, small organic molecule can catalyze 2e-ORR as efficiently as the state-of-the-art catalysts based on mercury-precious metal alloys. We propose different mechanisms of dioxygen electroreduction based on density functional theory calculations, which correlate activity with calculated standard reduction potential of reaction intermediates

Detection Technologies for Reactive Oxygen Species: Fluorescence and Electrochemical Methods and Their Applications

Reactive oxygen species (ROS) have been found in plants, mammals, and natural environmental processes. The presence of ROS in mammals has been linked to the development of severe diseases, such as diabetes, cancer, tumors, and several neurodegenerative conditions. The most common ROS involved in human health are superoxide (O2•−), hydrogen peroxide (H2O2), and hydroxyl radicals (•OH). Organic and inorganic molecules have been integrated with various methods to detect and monitor ROS for understanding the effect of their presence and concentration on diseases caused by oxidative stress. Among several techniques, fluorescence and electrochemical methods have been recently developed and employed for the detection of ROS. This literature review intends to critically discuss the development of these techniques to date, as well as their application for in vitro and in vivo ROS detection regarding free-radical-related diseases. Moreover, important insights into and further steps for using fluorescence and electrochemical methods in the detection of ROS are presented

Structure of Fe–N_<i>x</i>–C Defects in Oxygen Reduction Reaction Catalysts from First-Principles Modeling

The structure of active sites in Fe-based nonprecious metal oxygen reduction reaction catalysts remains unknown, limiting the ability to follow a rational design paradigm for catalyst improvement. Previous studies indicate that N-coordinated Fe defects at graphene edges are the most stable such sites. Density functional theory is used for determination of stable potential oxygen reduction reaction active sites. Clusters of Fe–N_<i>x</i> defects are found to have N-coordination-dependent stability. Previously reported interedge structures are found to be significantly less stable than in-edge defect structures under relevant synthesis conditions. Clusters that include Fe–N₃ defects are found to spontaneously cleave the O–O bond