Investigation of hollow nitrogen-doped carbon spheres as non-precious Fe-N-4 based oxygen reduction catalysts

The development of inexpensive non-precious oxygen reduction catalysts has become one of the most important efforts in polymer electrolyte membrane fuel cells. In this report, we synthesized a non-precious electrocatalyst from a single precursor, iron(iii) diethylene triaminepentaacetate, using a heat-treatment effect to prepare an active catalyst. A series of catalysts were prepared at different temperatures leading to different degrees of graphitization, heteroatom content and activity. In 0.1 M KOH electrolyte solution, the oxygen reduction reaction (ORR) onset potential of the HNCS71 catalyst was as high as 0.97 V, and half-wave potentials were only 20 mV lower than those for Pt/C. X-ray absorption measurements of the Fe K-edge showed the structure of Fe-N<inf>4</inf> centers, formed in HNCS71, which were responsible for the ORR activity. An alkaline exchange membrane fuel cell fabricated with HNCS71 as the cathode was tested in a H<inf>2</inf>-O<inf>2</inf> single cell and showed a maximum power density of ∼68 mW cm-2. The 100 hour fuel cell durability test of the HNCS71 cathode showed a decay in the current density of about 14% at 0.4 V. Therefore, the HNCS catalyst appears to be a promising new class of non-precious catalysts for fuel cell applications. © 2015 Royal Society of Chemistry.

Impact of hole scavengers on efficient photocatalytic hydrogen production

Hydrogen is one of the most promising alternative energy resources to replace fossil feedstocks, with so‐called “green” hydrogen, derived by water splitting (WS) using renewable electricity or sunlight, the most sustainable. Photocatalytic hydrogen production, in which sunlight is the sole energy input, has been extensively studied, and requires the creation of photogenerated excitons (through irradiation of semiconductors) and their transport to aqueous media. Chemical scavengers, notably electron donating molecules, are widely used to quench photogenerated holes and thereby suppress exciton recombination which otherwise limits the hydrogen yield. Despite their prevalence, the role and significance of such scavengers (also termed sacrificial agents) in photocatalytic WS remains poorly understood, hindering their rational selection. This review focuses on the importance of electron donors in photocatalytic WS, and their participation in the reaction mechanism