Co–C–N Oxygen Reduction Catalysts Prepared by Combinatorial Magnetron Sputter Deposition

Abstract

Thin-film libraries of CoxnormalC1−x−ynormalNy ( 0<x<0.107 , 0.003<y<0.389 ) were prepared by combinatorial magnetron sputter deposition in an Ar∕normalN2 gas mixture followed by subsequent heat-treatment at 700, 800, or 1000°C in normalN2 atmosphere. By increasing the nitrogen partial pressure during sputtering, the nitrogen content was increased significantly in the as-sputtered libraries and more nitrogen remained in the libraries after heat-treatment. The catalytic activities of the libraries towards the oxygen reduction reaction (ORR) were studied using the rotating ring-disk electrode (RRDE) technique. CoxnormalC1−x−ynormalNy libraries heat-treated at 800°C with 0.004<x<0.105 and 0.026<y<0.097 showed good catalytic activities towards ORR in 0.1M HClO4 solution at room temperature. The heating temperature that induces the onset of catalytic activity coincides with the temperature at which both substantial nitrogen release from the originally amorphous films and the formation of graphitic carbon and β-Co occurs. This temperature varies significantly with both the Co and N content in the films. The production of normalH2normalO2 and the corrosion stability of the libraries are also discussed.

The effect of boron doping into Co-C-N and Fe-C-N electrocatalysts on the oxygen reduction reaction

“…2 are guides to the eye which have been drawn by analogy to the carefully measured variation of N content with heating temperature for Fe-C-N and Co-C-N materials as presented in refs. [21] and [22]. The nitrogen content is reduced to the same extent during heat-treatment presumably because both Co-C-N-B and Fe-C-N-B libraries have a similar metal loading between 12 and 14 at.%.…”

“…The fact that Co and Fe are graphitization catalysts explains the higher release of nitrogen upon heating [28]. The nitrogen content in the C-N-B library also decreases with increasing annealing temperature, but the release occurs at higher temperature and hence the typical "knee-point" is observed at higher temperature [21][22][23].…”

“…In the past three years our combinatorial magnetron sputtering infrastructure was successfully used to systematically explore active compositions of non-noble metal catalysts for the oxygen reduction reaction [21][22][23]. Thin film Fe-C-N and Co-C-N libraries have been prepared and studied as catalysts [21,22].…”

“…Thin film Fe-C-N and Co-C-N libraries have been prepared and studied as catalysts [21,22]. Since hexagonal boron-nitride is isostructural and isoelectronic with graphite [24] we decided to incorporate boron into Fe-C-N and Co-C-N libraries in an attempt to increase the nitrogen content and hence the catalytic activity.…”

Experimental and theoretical modeling of Fe-, Co-, Cu-, Mn-based electrocatalysts for oxygen reduction

“…It is nearly identical. The iron is Transition metal (Co), carbon and nitrogen containing catalysts produced by sputtering by Yang et al [16] produced hydrogen peroxide with 60-80% yield, indicating that multi-electron transfer is not working. The catalysts discussed here generated hydrogen peroxide with less than 10%, indicating that most catalytic centers have multi-electron transfer properties.…”