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...

Iridium–nickel (Ir–Ni) and iridium–cobalt (Ir–Co) nanowires have been synthesized by galvanic displacement and studied for their potential to increase the performance and durability of electrolysis systems. Performances of Ir–Ni and Ir–Co nanowires for the oxygen evolution reaction (OER) have been measured in rotating disk electrode half-cells and single-cell electrolyzers and compared with commercial baselines and literature references. The nanowire catalysts showed improved mass activity, by more than an order of magnitude compared with commercial Ir nanoparticles in half-cell tests. The nanowire catalysts also showed greatly improved durability, when acid-leached to remove excess Ni and Co. Both Ni and Co templates were found to have similarly positive impacts, although specific differences between the two systems are revealed. In single-cell electrolysis testing, nanowires exceeded the performance of Ir nanoparticles by 4–5 times, suggesting that significant reductions in catalyst loading are possible without compromising performance.

For the first time, extended nanostructured catalysts are demonstrated with both high specific activity (>6000 μA cm Pt –2 at 0.9 V) and high surface areas (>90 m 2 g Pt –1 ). Platinum–nickel (Pt—Ni) nanowires, synthesized by galvanic displacement, have previously produced surface areas in excess of 90 m 2 g Pt –1 , a significant breakthrough in and of itself for extended surface catalysts. Unfortunately, these materials were limited in terms of their specific activity and durability upon exposure to relevant electrochemical test conditions. Through a series of optimized postsynthesis steps, significant improvements were made to the activity (3-fold increase in specific activity), durability (21% mass activity loss reduced to 3%), and Ni leaching (reduced from 7 to 0.3%) of the Pt—Ni nanowires. These materials show more than a 10-fold improvement in mass activity compared to that of traditional carbon-supported Pt nanoparticle catalysts and offer significant promise as a new class of electrocatalysts in fuel cell applications.

Solid metal oxides for carbon capture exhibit reduced adsorption capacity following high-temperature exposure, due to surface area reduction by sintering. Furthermore, only low-coordinate corner/edge sites on the thermodynamically stable (100) facet display favorable binding toward CO, providing inherently low capacity. The (111) facet, however, exhibits a high concentration of low-coordinate sites. In this work, MgO(111) nanosheets displayed high capacity for CO, as well as a ∼65% increase in capacity despite a ∼30% reduction in surface area following sintering (0.77 mmol g @ 227 m g vs 1.28 mmol g @ 154 m g). These results, unique to MgO(111), suggest intrinsic differences in the effects of sintering on basic site retention. Spectroscopic and computational investigations provided a new structure-activity insight: the importance of high-temperature activation to unleash the capacity of the polar (111) facet of MgO. In summary, we present the first example of a faceted sorbent for carbon capture and challenge the assumption that sintering is necessarily a negative process; here we leverage high-temperature conditions for facet-dependent surface activation.

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