Using Earth-Abundant Cobalt for Energy Conversion and Storage

Hanguang Zhang working in Gang Wu lab

CBE PhD candidate Yanghua He of the Wu research group was recently published in Energy and Environmental Science, the Journal of the Royal Society of Chemistry.

Published November 14, 2018

CBE PhD candidate Yanghua He has developed a cobalt catalyst for electrochemical energy technology that solves environmental concerns.  Her research interest focuses on exploring advanced electrocatalyst designs and synthesis strategies using earth-abundant elements for energy conversion applications such as metal-air batteries and fuel cells.

Platinum-group-metal (PGM)-free catalysts have been considered as a long-term goal for advanced fuel cell technologies with recent investments from both The United States Department of Energy (DOE) and agencies from other nations. Currently, the primary issue of PGM-free catalysts is the catalysts' stability with H2O2 as by-products from potential Fenton reactions during the Oxygen Reduction Reaction (ORR) in acid media. Co-based catalysts emerge as ideal candidates for Pt-free and Fe-free catalysts in challenging acidic media.

HRTEM, HAADF-STEM and STEM-EDS elemental mappings

 HRTEM, HAADF-STEM and STEM-EDS elemental mappings for (A) surfactant-free Co-ZIF-8 precursor, (B) Co-ZIF-8@F127 precursor, (C) surfactant-free Co–N–C catalyst and (D) Co–N–C@F127 catalyst.

Comparing with Fe-N-C catalysts, most Co-N-C catalysts still suffer from inactivity and high yields of H2O2 during the ORR in acid media. Yanghua's research focuses on improving these hindering characteristics of Co-N-C catalysts. With her collaborators, Yanghua and her team reported an efficient surfactant-assisted confinement pyrolysis strategy to effectively control the synthesis of CoN4active sites with significantly increased in power density. As expected, the Co-N-C@F127 catalyst exhibits an unprecedented ORR activity with a half-wave potential (E1/2) of 0.84 V (vs. RHE) as well as enhanced stability in the corrosive acidic media. The catalyst also demonstrates high initial performance with a power density of 0.87 W cm-2 along with encouraging durability in H2-O2 fuel cells. The performance of the atomically dispersed Co site catalyst approaches that of the Fe-N-C catalysts. Unlike other Co catalysts, this new atomically dispersed Co-N-C@F127 catalyst is deemed to contain substantial CoN2+2 sites, which are active and thermodynamically favorable for the four-electron ORR pathway. At this moment, the catalyst invented by Yanghua and her collaborators exhibits the highest ORR performance  reported for PGM-free and Fe-free catalysts.

This finding is published in Energy & Environmental Science, which is a monthly journal published by the Royal Society of Chemistry with an impact factor over 30. [Read the full paper]