Microbial synthesis of highly dispersed nano-Pd electrocatalyst for oxygen reduction reaction.

Microbial fabrication is eco-friendly for nobel-metal catalysts typically used in proton exchange membrane fuel cell (PEMFC). In our study, nano-Pd electrocatalysts were successfully prepared by using three Shewanella s as precursors through hydrogen reduction (200 °C) and carbonization (800 °C). The analysis revealed that the catalysts showed outstanding ORR electrocatalytic performance via a predominant four-electron oxygen reduction pathway in alkaline medium. The best performance was obtained for Pd/HNC-32, which showed a mass activity at 0.526 A mg−1, 3.78 times higher than that of commercial Pd/C. Shewanella putrefaciens CN-32 was a more effective Pd-adsorbent. The enhanced performance can be ascribed to the small Pd-particle size and uniform dispersion on microbial support, which results from stronger hydrophilicity of Shewanella putrefaciens CN-32. The content of nitrogen is another key to the performance of Pd/HNC-32. This study developed a promising strategy for screening microbial strains for electrocatalyst fabrication. • Carboxyl is a key surface functional group, which determines the positive ability of Shewanella s to adsobing Pd2+. • Good wetting performances of cells would effectively avoid the agglomeration of Pd particles supported on Shewanella s. • Pd/HNC-32 has best catalytic performances due to smaller size of monodispersed Pd and high content of Pd and nitrogen. • CN-32 is optimal precursor of three Shewanella s for Pd electrocatalyst prepared via our convenient and environmental method. [ABSTRACT FROM AUTHOR]