Biological reduction of O2 to H2O justifies a serious look at heme as a potential O2 reduction reaction(ORR) catalyst for low temperature fuel cells.In this study,a novel non-platinum electrocatalyst for ORR was prepared through hemin,which is hydrochloride of heme,supported on Black Pearls 2000 carbon black(Hm-BP) pyrolyzed at 700-900℃ in Ar atmosphere.The physical and electrocatalytic properties of as-prepared catalysts were characterized by TGA,XRD,XPS,TEM,rotating disk electrode(RDE) and rotating ring disk electrode(RRDE).It has found that the catalyst treated at 750℃(Hm-BP-750) exhibits the best property among the Hm-BP catalysts prepared.The onset potential of ORR on the Hm-BP-750 at 30℃ was measured ca.0.90 V(vs.RHE) in 0.1 M H2SO4,and mass current density was reached 15.3 mA mg-1 at 0.75 V.It has revealed that O2 could be reduced directly to water in a 4e process between 0.9 and 0.83V,and the yield of H2O2 was 0-18% in the potential range of 0.83-0.63 V.This methanol-tolerant catalyst also presents excellent stability in medium-term test of direct methanol fuel cell at 80℃.
Qiang WangZhiYou ZhouDeJun ChenJianLong LinFuSheng KeGuiLiang XuShiGang Sun
Fast surface dynamic processes of thiocyanate adsorbed on a nanostructured Pt microelectrode were studied by in situ step-scan time-resolved microscope FTIR spectroscopy(in situ SSTR-MFTIRS) at a time resolution of 100 s.It was found that SCN adsorbs preferentially on Pt surface through N atom at low potential,while through S atom at high potential.The potential-induced orientation conversion between N-and S-bounded forms is very reversible,and occurs only within 2 ms after potential alternation.However,the rate constant(4*103s-1) of conversion from N-to S-bounded adsorption is nearly double to that of the reverse process(2*103s-1).The difference in kinetics of two processes may be explained through the hard-soft acid-base principle.
Polymer electrolyte membrane fuel cells (PEMFC) have been recognized as a significant power source in future energy systems based on hydrogen. The current PEMFC technology features the employment of acidic polymer electrolytes which, albeit superior to electrolyte solutions, have intrinsically limited the catalysts to noble metals, fundamentally preventing PEMFC from widespread deployment. An effective solution to this problem is to develop fuel cells based on alkaline polymer electrolytes (APEFC), which not only enable the use of non-precious metal catalysts but also avoid the carbonate-precipitate issue which has been troubling the conventional alkaline fuel cells (AFC). This feature article introduces the principle of APEFC, the challenges, and our research progress, and focuses on strategies for developing key materials, including high-performance alkaline polyelectrolytes and stable non-precious metal catalysts. For alkaline polymer electrolytes, high ionic conductivity and satisfactory mechanical property are difficult to be balanced, therefore polymer cross-linking is an ultimate strategy. For non-precious metal catalysts, it is urgent to improve the catalytic activity and stability. New materials, such as transition-metal complexes, nitrogen-doped carbon nanotubes, and metal carbides, would become applicable in APEFC.
