Advances in the development of Pt-group metal-free (PGM-free) catalysts for oxygen reduction reaction in fuel cells produced active catalysts that allow to reduce the performance gap to the incumbent Ptbased materials. However, the utilization of the state-of-the-art PGM-free catalysts in commercial applications is currently impeded by their relatively low durability. Methods designed to study catalyst degradation in operating fuel cells are critical for the understanding and ultimately solving the durability issues. This work is the first report on the use of Fourier-transformed alternating current voltammetry (FTacV) as an electrochemical method for accurately quantifying the electrochemical site density of PGMfree ORR catalysts, and following their degradation during the operation of polymer electrolyte fuel cells. Using this method we were capable of detecting changes in performance of electrochemically active species (electrocatalytic centers in this case), allowing us, for the first time, to calculate the electrochemical active site density (EASD) which is necessary for the elucidation of the degradation mechanisms of PGM-free ORR catalysts in situ fuel cells.

In the search for replacement of the platinum‐based catalysts for fuel cells, MN4 molecular catalysts based on abundant transition metals play a crucial role in modeling and investigation of the influence of the environment near the active site in platinum‐group metal‐free (PGM‐free) oxygen reduction reaction (ORR) catalysts. To understand how the ORR activity of molecular catalysts can be controlled by the active site structure through modification by the pH and substituent functional groups, the change of the ORR onset potential and the electron number in a broad pH range was examined for three different metallocorroles. Experiments revealed a switch between two different ORR mechanisms and a change from 2e− to 4e− pathway in the pH range of 3.5‐6. This phenomenon was shown by density functional theory (DFT) calculations to be related to the protonation of the nitrogen atoms and carboxylic acid groups on the corroles indicated by the pKa values of the protonation sites in the vicinity of the ORR active sites. Control of the electron‐withdrawing nature of these groups characterized by the pKa values could switch the ORR from the H+ to e− rate‐determining step mechanisms and from 2e− to 4e− ORR pathways and also controlled the durability of the corrole catalysts. The results suggest that protonation of the nitrogen atoms plays a vital role in both the ORR activity and durability for these materials and that pKa of the N atoms at the active sites can be used as a descriptor for the design of high‐performance, durable PGM‐free catalysts.

Four β-pyrrole-substituted cobalt(iii) corroles were studied as electrocatalysts for the oxygen reduction reaction. The results disclose high dependence of the corrole's performance on its substituents, but once adsorbed on a high surface area carbon, this effect vanishes, resulting in a better catalytic performance than most well-defined molecular electrocatalysts for this reaction.

Three cobalt(III) complexes of regioisomeric trans-A 2 B-corroles were designed and efficiently synthesized. The corroles were adsorbed on smooth glassy carbon (GC) and black pearls 2000 (BP2000), high-surface-area carbon. Albeit spatially separated from the cobalt reaction center, the position of COOH group has a profound influence on the oxygen reduction reaction electrocatalytic reactivity when on GC, whereas on BP2000, a significant increase in selectivity toward the 4-electron reduction was observed in an alkaline environment. This is attributed to the wetting properties of the hydrophobic pores of BP2000, which considerably lower the dielectric constant in the pore water environment, stabilize the charged OOH − intermediate, and favor the 4-electron reduction pathway with the cobalt-bis-pentafluorophenyl (phenyl-para-carboxylic acid), when compared to analogous corroles with the COOH group at the ortho-and meta-positions.

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Alkaline electrolyte membrane electrolyzers are a promising technology to efficiently produce clean hydrogen without the use of critical raw materials. At the heart of these electrolyzers are the electrocatalysts, which facilitate the cathodic and anodic reactions, with the latter oxygen evolution reaction (OER) being the most sluggish. In recent years, aerogels have become a very well-studied class of materials due to their unique properties, including very high surface area. Until now, aerogels have not been used to catalyze the OER by themselves but were mainly considered catalyst supports. Here, mixed-metal nickel–iron oxide aerogels were synthesized with a modified epoxide route synthesis and tested as OER catalysts. Depending on the Ni/Fe ratio, they show very high catalytic activity and low overpotential to reach 10 mA cm–2 (at η = 380 mV). This activity is beyond that of the existing state-of-the-art platinum group metal-free OER catalysts.

Electrolyzer technologies are essential for the Hydrogen Economy scheme, and in order to drive the hydrogen production price down, their lifetimes need to be extended. One important parameter that has not been given enough attention in this context is catalyst durability. In this work, a durable platinum-group metal-free catalyst was developed for the hydrogen evolution reaction based on a porous, high-surface area molybdenum carbide aerogel. The molybdenum oxide aerogel was synthesized by a sol–gel method and carburized by methane treatment. A three-dimensional molybdenum carbide network was obtained by reacting the molybdenum oxide aerogel with a CH4/H2 mixture at 700 °C. Surface area measurement confirmed a substantial increase in the volume of micropores in the transition from oxide to carbide. The carbide aerogel has low density (<0.4 g/mL) with a relatively high surface area of 109 m2/g (reduced from 188 m2/g after methane treatment). The molybdenum carbide aerogel shows remarkable stability compared to the Pt/C catalyst, with only a 10 mV overpotential shift vs 100 mV for Pt/C after stability tests.

Molecular ORR catalysts based on metallo-corrole with the smallest meso-substituent reported to date, Co(iii)CF3-corrole, was synthesized and compared to the well-studied Co(iii)tpf-corrole when adsorbed on a high surface area carbon support.