Competition between Lattice Oxygen and Adsorbate Evolving Mechanisms in Rutile Ru-Based Oxide for the Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is the primary bottleneck for electrochemical splitting of water into H2. Developing robust and active OER electrocatalysts through understanding the OER mechanism is essential. However, the mechanism for OER is not yet well understood even for the most studied rutile Ru-based oxide, especially in a water-solvent environment. It is still disputed whether the adsorbate evolving mechanism (AEM) is competitive with the lattice oxygen mechanism (LOM). In this article, the AEM and LOM for OER in transition metal (TM)-doped rutile RuO2 with different ratios of TM and Ru are discussed through density functional theory + U calculation. In low TM doping concentration, the evolved O2 is generated through the AEM, and the OER activity is limited by the scaling relationship of OER intermediates. In higher TM doping concentration, the evolved O2 is generated through the LOM for Cu- or Ni-doped RuO2. We find that the distribution of Ru 4d and O 2p orbitals and the adsorption energy of H and O are the major factors that affect the conversion of AEM into LOM. By explicitly considering the water-solvent environment, the LOM can result in higher theoretical OER activity arising from the effects of hydrogen-bond networks

Nd₆Ir₂O₁₃ as an Efficient Electrocatalyst Boosts the Oxygen Evolution Reaction in Acidic Media

A highly active and robust electrocatalyst for the oxygen evolution reaction (OER) in acidic conditions is essential for proton-exchange membrane water electrolyzers. Herein, a novel Nd6Ir2O13 electrocatalyst was synthesized and first applied in acidic OER. During the OER, surface Nd atoms are leached out to form active hydrated IrOx; meanwhile, the coordination environment of Ir remains relatively stable. Benefiting from the low Ir content (26.4 wt %), Nd6Ir2O13 affords an Ir mass activity of 123.5 mA per mgIr at an overpotential of 300 mV, about 42-fold that of IrO2. Notably, Nd6Ir2O13 needs an ultralow overpotential of 291 mV to acquire a current density of 10 mA cm–2 and continuously catalyzes OER for 70,000 s with little overpotential increase, far beyond that of the benchmark IrO2 and most of the electrocatalysts for the acidic OER. This work opens a new type of Ir-based oxides with ultralow Ir content, which expands the acidic OER electrocatalyst family of multimetal oxides

Synergistic Effect of Electronic Particle–Support Interactions on the Ir-Based Multiheterostructure for Acidic Water Oxidation

Exploiting durable electrocatalysts with high specific activity for acidic water oxidation is a great challenge due to the high energy barrier for the multiple oxygen evolution reaction (OER) intermediates. Deliberately taking advantage of the synergistic effect of electronic particle–support interactions on both the particle and support may address this concern. Here, we deliberately design a multiheterostructure with an IrO2 shell-coated Ir core anchored on the Co3O4 framework as an efficient acidic OER electrocatalyst. Detailed characterizations (depth-resolved XPS, XANES, and EXAFS) of the electrocatalysts demonstrate that the electronic particle–support interactions lead to a unique electron transfer at the interface from IrO2 and Co3O4 to Ir. Such an electron transfer will result in compressed Ir–O bonds and Co–O bonds, thus simultaneously reducing free energies for OER intermediates on the surfaces of both IrO2 and Co3O4, sufficiently stimulating the synergistic effect to enhance OER activity and stability

Does the Oxidation of Nitric Oxide by oxyMyoglobin Share an Intermediate with the metMyoglobin-Catalyzed Isomerization of Peroxynitrite?

The reaction of nitric oxide with oxy-myoglobin (oxyMb) to form ferric myoglobin (metMb) and nitrate, and the metMb-catalyzed isomerization of peroxynitrite to nitrate, have long been assumed to proceed via the same iron-bound peroxynitrite intermediate (metMb­(OONO)). More recent research showed that the metMb-catalyzed isomerization of peroxynitrite to nitrate produces detectable amounts of nitrogen dioxide and ferryl myoglobin (ferrylMb). This suggests a mechanism in which the peroxynitrite binds to the metMb, ferrylMb is transiently generated by dissociation of NO₂, and nitrate is formed when the NO₂ nitrogen attacks the ferrylMb oxo ligand. The presence of free NO₂ and ferrylMb products reveals that small amounts of NO₂ escape from myoglobin’s interior before recombination can occur. Free NO₂ and ferrylMb should also be generated in the reaction of oxyMb with NO, if the common intermediate metMb­(OONO) is formed. However, this report presents a series of time-resolved UV/vis spectroscopy experiments in which no ferrylMb was detected when oxyMb and NO reacted. The sensitivity of the methodology is such that as little as 10% of the ferrylMb predicted from the experiments with metMb and peroxynitrite should have been detectable. These results lead to the conclusion that the oxyMb + NO and metMb + ONOO^– reactions do <i>not</i> proceed via a common intermediate as previously thought. The conclusion has significant implications for researchers that propose a possible role of oxyMb in intracellular NO regulation, because it means that toxic NO₂ and ferrylMb are not generated during NO oxidation by this species

Interface Engineering of Oxygen Vacancy-Enriched Ru/RuO₂–Co₃O₄ Heterojunction for Efficient Oxygen Evolution Reaction in Acidic Media

RuO2 is currently regarded as a benchmark electrocatalyst for water oxidation in acidic media. However, its wide application is still restricted by limited durability and high cost. Herein, we report a Ru/RuO2–Co3O4 catalyst for boosting the acidic oxygen evolution reaction catalytic performance via constructing a heterointerface between RuO2 and Co3O4 and vacancy engineering. The resulting Ru/RuO2–Co3O4 shows a 226 mV overpotential at 10 mA cm–2 and excellent stability with a small overpotential increase after continuous testing for 19 h, greatly surpassing that of commercial RuO2 in a 0.1 M HClO4 solution. Depth structure characterizations involved in XPS, XANES, and EXAFS indicate that the favorable catalytic performance of Ru/RuO2–Co3O4 is mainly ascribed to the interfacial charge transfer by heterojunction interfaces between Co species and Ru species. Co3O4 is adjacent to RuO2 and donates electrons, making the valence state of Ru lowered and the Ru–O covalency weakened, which greatly suppress the dissolution of Ru and thus enhance stability. Meanwhile, the existing oxygen vacancies improve the intrinsic catalytic activity. This study is highly expected to favor the design and synthesis of more highly efficient electrocatalysts applied in energy-related devices

Sm-Induced Symmetry-Broken Ru Centers for Boosting Acidic Water Oxidation

Ruthenium oxide (RuO2) as a promising acidic oxygen evolution reaction (OER) electrocatalyst for proton exchange membrane water electrolyzers still suffers from severe excessive oxidation and Ru dissolution, leading to the loss of activity. Herein, a Sm doping in amorphous/crystalline heterophase RuO2 (AC-Sm-RuO2) catalyst is designed for boosting the acidic OER catalytic performance by altering the electronic properties and number of active sites. The representative AC-Sm-RuO2 displays robust OER performance with an overpotential of 200 mV to achieve 10 mA cm–2, and significantly enhanced stability compared to synthesized RuO2 (S-RuO2) and commercial RuO2 (Com. RuO2). Electrochemical measurements combined with advanced characterizations reveal that the high activity in AC-Sm-RuO2 originated from the symmetry-broken Ru active sites, which lowers the formation energy barrier of *OOH; meanwhile, the improved stability arises from the strong interplay within the local Ru–O–Sm units and the characteristics of the amorphous/crystalline hybrid. This work emphasizes the effective means to design high-performance acidic OER catalysts via the synergy of microstructure symmetry disturbance and crystal phase engineering

Boosting Oxygen Reduction Catalysis with N‑doped Carbon Coated Co₉S₈ Microtubes

Herein, nitrogen-doped carbon coated hollow Co₉S₈ microtubes (Co₉S₈@N–C microtubes) are prepared through a facile solvothermal procedure, followed by dopamine polymerization process together with a post-pyrolysis which present excellent electrocatalytic activity for oxygen reduction reaction (ORR). The Co₉S₈ within the hollow Co₉S₈@N–C microtubes presents a well-defined single-crystal structure with dominated (022) plane. To obtain desired electrocatalyst, the annealing temperature and the thickness of carbon layer tuned by changing the dopamine concentration are optimized systematically. The electrochemical results demonstrate that the coordination of the N-doped carbon layer, exposed (022) plane, and hollow architecture of Co₉S₈ microtubes calcined at 700 °C affords outstanding ORR performance to Co₉S₈@N–C microtubes. The moderate thickness of the carbon layer is crucial for improving ORR activity of Co₉S₈@N–C microtubes, while increasing or decreasing the thickness would result in activity decrease. More importantly, the N-doped carbon layer can protect inner Co₉S₈ from undergoing aggregation and dissolution effectively during the ORR, resulting in excellent electrocatalytic stability

Interface Engineering of MoS₂ for Electrocatalytic Performance Optimization for Hydrogen Generation via Urea Electrolysis

Developing highly efficient and low-cost nonprecious electrocatalysts for hydrogen evolution reaction (HER) has a pivotal impact on the emergence of hydrogen energy. Herein, quaternary electrocatalyst characterized by abundant interfaces supported on carbon cloth (denoted as Mo–Co–S–Se/CC) is designed through a facile solvothermal and post-low-temperature selenylation process, which delivers excellent catalytic performances in HER, oxygen evolution reaction (OER), and urea oxidation reaction (UOR) in alkaline electrolyte. Benefiting from the rich interfaces, the designed catalyst delivers current densities of 10 and 100 mA cm–2 with low overpotentials of 58 and 167 mV, respectively, and small Tafel slope of 84 mV dec–1 for HER. For the anodic OER, only 350 mV overpotential is needed to drive 100 mA cm–2 in 1 M KOH solution. Moreover, Mo–Co–S–Se/CC also presents remarkable catalytic activity for UOR in 1 M KOH solution, which provides another way to substitute the sluggish OER to reduce the cost of hydrogen production. As a proof of concept, overall water-splitting tests are measured with Mo–Co–S–Se/CC as both anode and cathode, respectively, in 1 M KOH solution with 0.5 M urea; only 1.4 V is required to drive 10 mA cm–2, much lower than that for urea-free electrolyte with 1.62 V