Unraveling the Link between Catalytic Activity and Agglomeration State with Scanning Electrochemical Microscopy and Atomic Force Microscopy

Abstract

In this article, we set up a methodology to investigate the relationship between the catalytic activity and the agglomeration state of platinum group metal-free ORR catalysts. To this end, we have developed a statistical approach based on scanning electrochemical microscopy (SECM) and atomic force microscopy (AFM). Two catalysts are investigated at very low loadings in order to access their intrinsic activity. Differences in terms of dispersion, stability of the inks, and adherence on the substrate are observed, highlighting the importance of measuring the exact amount and agglomeration state of the materials under study. The agglomeration state of the deposits measured by AFM explains the differences in activity measured by SECM. The performances of the catalysts are compared, and the contributions of the intrinsic activity and the agglomeration state are identified. This work paves the way toward various applications ranging from the benchmarking of new catalysts to the optimization of an ink formulation, for ORR and beyond.

Scrutinizing Intrinsic Oxygen Reduction Reaction Activity of a Fe−N−C Catalyst via Scanning Electrochemical Cell Microscopy

“…The catalyst powder was synthesized via a procedure described in a previous work [30] . Thereafter, the ink was prepared by dispersing 20 mg of catalyst powder into a 1.175 mL mixture of isopropanol and water (3 : 1 ratio) and 24 mg Nafion (5 % in weight after drying), leading to a concentration of 17 mg mL −1 .…”

“…The catalyst powder was synthesized via a procedure described in a previous work. [30] Thereafter, the ink was prepared by dispersing 20 mg of catalyst powder into a 1.175 mL mixture of isopropanol and water (3 : 1 ratio) and 24 mg Nafion (5 % in weight after drying), leading to a concentration of 17 mg mL À 1 . Subsequently, after adding ~15 g of Zirconium beads, the ink was treated 40 minutes on an IKA ULTRA-TURRAX® Tube Drive for an initial breaking of agglomerates, followed by ball milling for one week in an IKA ROLLER 6 shaker.…”

Single Entity Electrocatalysis

“…For example, convoluted in SECM measurements of single entities on a substrate is the distance between the electrocatalyst/substrate and the tip electrode . Therefore, there has been increasing interest in pairing SECM with other techniques, like AFM , or scanning ion-conductance microscopy, or changing the SECM measuring procedure, such as collecting approach curves for each lateral point to circumvent these limitations and simultaneously provide maps of the substrate’s surface topography and electrocatalytic activity. Leonard and co-workers have developed fuzzy logic algorithms that may also be useful in ensuring a constant height from the entity to the tip .…”