Octahedral spinel electrocatalysts for alkaline fuel cells.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 31727846.
- Also identified by DOI 10.1073/pnas.1906570116 and PMC identifier 6900538.
- No licence information is recorded for this record.
- Because redistribution is not established, this page shows the abstract only. Follow the links below for the full text.
Abstract
Designing high-performance nonprecious electrocatalysts to replace Pt for the oxygen reduction reaction (ORR) has been a key challenge for advancing fuel cell technologies. Here, we report a systematic study of 15 different AB<sub>2</sub>O<sub>4</sub>/C spinel nanoparticles with well-controlled octahedral morphology. The 3 most active ORR electrocatalysts were MnCo<sub>2</sub>O<sub>4</sub>/C, CoMn<sub>2</sub>O<sub>4</sub>/C, and CoFe<sub>2</sub>O<sub>4</sub>/C. CoMn<sub>2</sub>O<sub>4</sub>/C exhibited a half-wave potential of 0.89 V in 1 M KOH, equal to the benchmark activity of Pt/C, which was ascribed to charge transfer between Co and Mn, as evidenced by X-ray absorption spectroscopy. Scanning transmission electron microscopy (STEM) provided atomic-scale, spatially resolved images, and high-energy-resolution electron-loss near-edge structure (ELNES) enabled fingerprinting the local chemical environment around the active sites. The most active MnCo<sub>2</sub>O<sub>4</sub>/C was shown to have a unique Co-Mn core-shell structure. ELNES spectra indicate that the Co in the core is predominantly Co<sup>2.7+</sup> while in the shell, it is mainly Co<sup>2+</sup> Broader Mn ELNES spectra indicate less-ordered nearest oxygen neighbors. Co in the shell occupies mainly tetrahedral sites, which are likely candidates as the active sites for the ORR. Such microscopic-level investigation probes the heterogeneous electronic structure at the single-nanoparticle level, and may provide a more rational basis for the design of electrocatalysts for alkaline fuel cells.