Highly Active and Durable Non-Precious Metal Catalyst for the Oxygen Reduction Reaction in Acidic Medium

Abstract

Polymer electrolyte fuel cells exhibit high potentials at the cathode during start-stop cycles in automotive applications, which leads to carbon support corrosion, and concomitant loss of electrocatalytic activity. In this study, carbon nanomaterials (CNM), predominantly composed of nitrogen doped multi-walled carbon nanotubes (N-MWCNTs) with encapsulated cobalt nanoparticles, were synthesized in-situ by the solid-state pyrolysis (SSP) of melamine and cobalt Oxide (Co3O4). The best formulation of the catalyst exhibited an ORR activity of of 2.3 mA cm−2 at 0.75 V vs. RHE (4.6 mA mg−1). The role played by cobalt to complete the active site was demonstrated as follows: Upon complexing the cobalt site with bipyridine, the ORR onset potential decreased by ∼90 mV. The stability of the above non-precious metal (NPM) catalyst was studied through accelerated stress tests (ASTs) designed to mimic load cycling and start-stop cycling protocols, wherein the catalyst was exposed to high anodic potentials (up to 1.5 V vs. RHE) in an acidic medium. In rotating disk electrode mode, the ORR polarization curve shifted to more negative values by about 20 mV and 14 mV, respectively, after the load cycling and start-stop cycling AST protocols, suggesting high stability. Similar stability was observed in fuel cell mode.

A Stable Graphitic, Nanocarbon‐Encapsulated, Cobalt‐Rich Core–Shell Electrocatalyst as an Oxygen Electrode in a Water Electrolyzer

“…[41] Additionally, the deconvoluted Co2p high-resolution spectrum (Figure 3D) exhibited two bands of metallic cobalt at 778.2 eV and 793.3 eV with a ~15 eV binding energy difference, which can be readily ascribed to Co2p 3/2 and Co2p 1/2 , respectively. [42] Noticeably, two prominent bands were exhibited at 780.4 eV and 796.1 eV with two broad shake-up satellites bands, and these were attributed to the Co 2+ oxidation states. [43] Most likely, the limited depth of the XPS analysis resulted in the Co 2+ states due to the surface oxidation of cobalt via the absorbed oxygen/hydroxides and Co-N interactions.…”

Robust Co‐Embedded Nitrogen Doped Carbon Catalyst for Oxygen Reduction Reaction in Proton Exchange Membrane Fuel Cell

“…Compared to reported fuel cell performance with Co−N−C catalysts, CoNC 3–1 cathode catalysts exhibited higher performance in terms of power density than acidic fuel cell with Co atom and N co‐doped carbon nanofibers, Co−N/CNFs (4 mg cm −2 , 16 mW cm −2 ) [40] and Co based MNC, Co−CNM‐120 min (3 mg cm −2 , 30 mW cm −2 ) [41] cathode catalysts. The cell exhibited lower power density as compared to Co−N−C cathode catalyst reported by Dombrovskis et al.…”

Metal‐Nitrogen‐Carbon Cluster‐Decorated Titanium Carbide is a Durable and Inexpensive Oxygen Reduction Reaction Electrocatalyst

“…Higher durability in Pt-based ORR catalysts has been obtained by dispersing Pt nanoparticles over corrosion-resistive supports, such as doped TiO 2 , doped SnO 2 , and other metal oxides that can withstand the voltage spikes during start-up/ shut-down cycles. [29][30][31][32][33][34][35][36] In TMN-catalysts, since the TMN-clusters are directly embedded in the matrix, there is a strong effect of the matrix on the stability and ORR activity of the embedded clusters. [37,38] Given the large choice of available TMN clusters coupled with a modest selection of available stable electrocatalyst matrices, [9,39] there is a need for a rational design approach that accounts for active site-matrix interactions to enable efficient identification of TMN cluster/matrix systems having the most promising combination of ORR activity and durability.…”