Nine non-noble-metal catalysts (NNMCs) from five different laboratories were investigated for the catalysis of O(2) electroreduction in an acidic medium. The catalyst precursors were synthesized by wet impregnation, planetary ball milling, a foaming-agent technique, or a templating method. All catalyst precursors were subjected to one or more heat treatments at 700-1050 degrees C in an inert or reactive atmosphere. These catalysts underwent an identical set of electrochemical characterizations, including rotating-disk-electrode and polymer-electrolyte membrane fuel cell (PEMFC) tests and voltammetry under N(2). Ex situ characterization was comprised of X-ray photoelectron spectroscopy, neutron activation analysis, scanning electron microscopy, and N(2) adsorption and its analysis with an advanced model for carbonaceous powders. In PEMFC, several NNMCs display mass activities of 10-20 A g(-1) at 0.8 V versus a reversible hydrogen electrode, and one shows 80 A g(-1). The latter value corresponds to a volumetric activity of 19 A cm(-3) under reference conditions and represents one-seventh of the target defined by the U.S. Department of Energy for 2010 (130 A cm(-3)). The activity of all NNMCs is mainly governed by the microporous surface area, and active sites seem to be hosted in pore sizes of 5-15 A. The nitrogen and metal (iron or cobalt) seem to be present in sufficient amounts in the NNMCs and do not limit activity. The paper discusses probable directions for synthesizing more active NNMCs. This could be achieved through multiple pyrolysis steps, ball-milling steps, and control of the powder morphology by the addition of foaming agents and/or sulfur.

Insufficient catalytic activity and durability are key barriers to the commercial deployment of low temperature polymer electrolyte membrane (PEM) and direct-methanol fuel cells (DMFCs). Recent observations suggest that carbon-based catalyst support materials can be systematically doped with nitrogen to create strong, beneficial catalyst-support interactions which substantially enhance catalyst activity and stability. Data suggest that nitrogen functional groups introduced into a carbon support appear to influence at least three aspects of the catalyst/support system: 1) modified nucleation and growth kinetics during catalyst nanoparticle deposition, which results in smaller catalyst particle size and increased catalyst particle dispersion, 2) increased support/catalyst chemical binding (or ''tethering''), which results in enhanced durability, and 3) catalyst nanoparticle electronic structure modification, which enhances intrinsic catalytic activity. This review highlights recent studies that provide broad-based evidence for these nitrogen-modification effects as well as insights into the underlying fundamental mechanisms.

Nitrogen modification of carbon structures is making a vast impact across the scientific community, specifically in the realms of energy and sustainability.

Unsupported iridium (Ir) nanoparticles, that serve as standard oxygen evolution reaction (OER) catalysts in acidic electrolyzers, were investigated for electrochemical performance and durability in rotating disk electrode (RDE) half-cells. Fixed potential holds and potential cycling were applied to probe the durability of Ir nanoparticles, and performance losses were found to be driven by particle growth (coarsening) at moderate potential (1.4 to 1.6 V) and Ir dissolution at higher potential (≥1.8 V Hydrogen is a major commodity chemical with approximately 2% of U. S. used energy going through a hydrogen pathway, primarily for ammonia production (agriculture) and the upgrading of crude oil (transportation). The majority of hydrogen in the US is produced from natural gas by steam methane reformation.1 While electrochemical water splitting currently represents a small percentage of hydrogen production, it is expected to have a growing role as costs decrease. 2Although the commercial competitiveness of electrolysis is currently limited by feedstock costs, catalyst cost and durability will become increasingly important as electrolyzers move toward low cost, intermittent, renewable sources of electricity such as wind and solar. 3,4 Acidic electrolyzers typically use iridium (Ir) in the oxygen evolution reaction (OER) as this material exhibits both reasonable activity and stability.5 Platinum and ruthenium have also been investigated as alternatives. Platinum, however, requires a higher overpotential (lower efficiency) and ruthenium has durability (dissolution) concerns. [6][7][8] Efforts to develop improved OER catalysts for acidic electrolyzers typically focus on supporting Ir oxide on titania 9-13 or alloying Ir with platinum, ruthenium, or other transition metal oxides [14][15][16][17][18][19][20][21][22][23] to improve durability and performance. Density functional theory studies have correlated trends in the OER activity of metal oxides to the adsorption energies of surface oxygen species, suggesting future directions for improving OER catalysts.24 Strasser et al. also examined the intrinsic activity of Ir, platinum, and ruthenium polycrystalline metals and nanoparticles in rotating disk electrode (RDE) half-cells, using carbon monoxide to determine catalyst surface areas.6 Efforts exploring OER catalysts, however, pale in comparison to the efforts expended in the pursuit of fuel cell catalysts for the oxygen reduction reaction (ORR). Specifically, the fuel cell community has established baselines and protocols for the performance and durability of ORR catalysts. [25][26][27][28] No such protocols or baselines currently exist for OER catalysts.This study presents data from several different commercial suppliers of unsupported and supported Ir and Ir oxide catalysts, and investigates the intrinsic activity of Ir in RDE half-cells, evaluating both performance and durability while presenting the data under standardized conditions. The modes of losses for Ir nanoparticles under specific testing protocols are present...