To propel the commercialization of fuel cells, the development of efficient nonprecious metal catalysts, specifically cathodic oxygen reduction catalysts, is turning into reality because the great advancements have been made on nitrogen-doped carbon materials recently. In this study, we demonstrated that nitrogen-doped hollow carbon nanoparticles (N-HCNPs) exhibit excellent electrocatalytic performance for oxygen reduction reaction (ORR) in alkaline fuel cells. Cyclic voltammetry and rotating ring-disk electrode voltammetry showed that the ORR activity of N-HCNPs approaches that of commercial Pt–C catalyst and is much better compared with nitrogen-free counterparts due to the incorporation of nitrogen atoms into graphitic structures. Kinetic studies indicated that the involvement of nitrogen induces a totally different oxygen adsorption mechanism and a four-electron dominated reaction pathway for N-HCNPs in comparison with nitrogen-free HCNPs, very similar to the observations in Pt–C. Moreover, N-HCNPs exhibited good operation stability and excellent tolerance to methanol crossover and CO poisoning for ORR superior to that of Pt–C. Our findings suggest that N-HCNPs catalyst is a promising alternative for the Pt-based catalysts in fuel cells.

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Photoelectrochemical sensors were developed for the rapid detection of oxidative DNA damage induced by Fe2+ and H2O2 generated in situ by the enzyme glucose oxidase. The sensor is a multilayer film prepared on a tin oxide nanoparticle electrode by layer-by-layer self-assembly and is composed of separate layers of a photoelectrochemical indicator, DNA, and glucose oxidase. The enzyme catalyzes the formation of H2O2 in the presence of glucose, which then reacts with Fe2+ and generates hydroxyl radicals by the Fenton reaction. The radicals attack DNA in the sensor film, mimicking metal toxicity pathways in vivo. The DNA damage is detected by monitoring the change of photocurrent of the indicator. In one sensor configuration, a DNA intercalator, Ru(bpy)2(dppz)2+ (bpy = 2,2'-bipyridine, dppz = dipyrido[3,2-a:2',3'-c]phenazine), was employed as the photoelectrochemical indicator. The damaged DNA on the sensor bound less Ru(bpy)2(dppz)2+ than the intact DNA, resulting in a drop in photocurrent. In another configuration, ruthenium tris(bipyridine) was used as the indicator and was immobilized on the electrode underneath the DNA layer. After oxidative damage, the DNA bases became more accessible to photoelectrochemical oxidation than the intact DNA, producing a rise in photocurrent. Both sensors displayed substantial photocurrent change after incubation in Fe2+/glucose in a time-dependent manner. And the detection limit of the first sensor was less than 50 microM. The results were verified independently by fluorescence and gel electrophoresis experiments. When fully integrated with cell-mimicking components, the photoelectrochemical DNA sensor has the potential to become a rapid, high-throughput, and inexpensive screening tool for chemical genotoxicity.

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