Ru-based oxygen evolution reaction (OER) catalysts show significant promise for efficient water electrolysis, but rapid degradation poses a major challenge for commercial applications. In this work, we explore several Ru-based pyrochlores (A 2 Ru 2 O 7 , A = Y, Nd, Gd, Bi) as OER catalysts and demonstrate improved activity and stability of catalytic Ru sites relative to RuO 2 . Furthermore, we combine complementary experimental and theoretical analysis to understand how the A-site element impacts activity and stability under acidic OER conditions. Amongst the A 2 Ru 2 O 7 studied herein, we find that a longer Ru-O bond and a weaker interaction of the Ru 4d and O 2p orbitals compared to RuO 2 results in enhanced initial activity. We observe that the OER activity of the catalysts changes over time and is accompanied by both A-site and Ru dissolution at different relative rates depending on the identity of the A-site. Pourbaix diagrams constructed using density functional theory (DFT) calculations reveal a driving force for this experimentally observed dissolution, indicating that all compositions studied herein are thermodynamically unstable in acidic OER conditions. Theoretical activity predictions show consistent trends between A-site cation leaching and OER activity. These trends coupled with Bader charge analysis suggest that dissolution exposes highly oxidized Ru sites that exhibit enhanced activity. Overall, using the stability number (mol O 2 evolved /mol Ru dissolved ) as a comparative metric, the A 2 Ru 2 O 7 materials studied in this work show substantially greater stability than a standard RuO 2 and commensurate stability to some Ir mixed metal oxides. The insights described herein provide a path to further enhance Ru catalyst activity and durability, ultimately improving the efficiency of water electrolyzers.

Advances in the separation and functionalization of single walled carbon nanotubes (SWCNT) by their electronic type have enabled the development of ratiometric fluorescent SWCNT sensors for the first time. Herein, single chirality SWCNT are independently functionalized to recognize either nitric oxide (NO), hydrogen peroxide (H2O2), or no analyte (remaining invariant) to create optical sensor responses from the ratio of distinct emission peaks. This ratiometric approach provides a measure of analyte concentration, invariant to the absolute intensity emitted from the sensors and hence, more stable to external noise and detection geometry. Two distinct ratiometric sensors are demonstrated: one version for H2O2, the other for NO, each using 7,6 emission, and each containing an invariant 6,5 emission wavelength. To functionalize these sensors from SWCNT isolated from the gel separation technique, a method for rapid and efficient coating exchange of single chirality sodium dodecyl sulfate‐SWCNT is introduced. As a proof of concept, spatial and temporal patterns of the ratio sensor response to H2O2 and, separately, NO, are monitored in leaves of living plants in real time. This ratiometric optical sensing platform can enable the detection of trace analytes in complex environments such as strongly scattering media and biological tissues.

Thomas F (2020) Nitride or Oxynitride? Elucidating the Composition-Activity Relationships in Molybdenum Nitride Electrocatalysts for the Oxygen Reduction Reaction. Chemistry of Materials.