Ultralow Ru-Induced Bimetal Electrocatalysts with a Ru-Enriched and Mixed-Valence Surface Anchored on a Hollow Carbon Matrix for Oxygen Reduction and Water Splitting

Abstract

Rational design of trifunctional electrocatalysts with robust efficiency used for oxygen reduction, oxygen evolution, and hydrogen evolution reactions (ORR, OER, and HER) is of significance to renewable energy conversion techniques, which remains a challenging issue. This study integrates dominant Co/Co3O4 with a small fraction of RuO2 and the CoRu alloy anchored on a hollow carbon matrix, originating from the novel Ru-doped hollow metal–organic framework (MOF) precursor, which is synthesized via tannic etching and ion exchange. Notably, the introduced ultralow Ru (1.28 wt %) not only generates new Ru-based species but also induces a Ru-enriched surface with abundant oxygen vacancies. Moreover, a suitable balance among different valencies of Co or Ru can be tuned by oxidation time, resulting in preferable Co2+ and Ru4+ species. Triggered by these unparalleled surface properties along with good conductivity, hollow structure, and the synergistic effect of multiple active sites, the resulting CoRu-O/A@hollow nitrogen-doped carbon (HNC) shows robust catalytic performance for ORR/OER/HER in an alkaline electrolyte. Typically, it exhibits a potential gap of 0.662 V for OER/ORR and enables an alkaline water electrolyzer with a cell voltage of 1.558 V at 10 mA cm–2. This work would serve as guidance for well construction of transition-metal-based trifunctional electrocatalysts by the MOF-assisted strategy or the modulation effects of low-content Ru.

Reconciling structure prediction of alloyed, ultrathin nanowires with spectroscopy

“…Nevertheless, relatively little work has been performed on RuCo alloys, which have been reported to be useful in applications, such as but not limited to batteries 23 and Fischer-Tropsch catalysts 24,25 in addition to electrocatalysts for the hydrogen evolution reaction (HER), 22,[26][27][28][29][30] the hydrogen oxidation reaction (HOR), 31 the oxygen reduction reaction (ORR), 32,33 and the oxygen evolution reaction (OER). 34 Results for RuCo alloys used as electrocatalysts have been especially promising, with the alloys frequently outperforming the Pt standards at lower overall costs.…”

Nanoscaled and Atomic Ruthenium Electrocatalysts Confined Inside Super‐Hydrophilic Carbon Nanofibers for Efficient Hydrogen Evolution Reaction

“…[36] The binding energies of 462.8 and 485.8 eV, and 466.1 and 488.5 eV were also deconvoluted, which belong to the oxidized 3p 3/2 and 3p 1/2 of Ru 2+ and Ru n+ (n > 2), respectively. [26,38] The ratio of nulvalent and oxidized Ru is estimated to be ≈8.2/1.8. The C 1s and Ru 3d spectra (Figure 4d) show that the C 1s peak was deconvoluted into four peaks: CC/CC (284.0 eV), CO/CN (285.7 eV), and NCO (288.3 eV); and the Ru 3d peak was fitted to Ru 0 3d 5/2 (280.2 eV), Ru 0 3d 3/2 (283.4 eV), Ru 2+ (280.8 eV), and Ru 4+ (281.4 eV).…”

“…Various Ru species, such as metal nanoparticles (NPs), alloys, oxides, phosphides, and selenides, have shown excellent HER activity. [19][20][21][24][25][26][27][28][29][30][31][32][33][34][35][36][37][38][39] Accumulative knowledge indicates that the size and dispersity of the active species have a significant influence on their electrocatalytic performance. [40][41][42][43][44] In particular, ultrasmall sizes (for example, sub-2 nm) and high dispersion are extremely attractive characteristics because they provide unique quantum confinement effects, increased specific surface area, and a high ratio of electrocatalytic active superficial atoms.…”

Critical Review, Recent Updates on Zeolitic Imidazolate Framework‐67 (ZIF‐67) and Its Derivatives for Electrochemical Water Splitting

“…Similarly, Li et al also fabricated Co-Ru oxide/alloy NPs embedded in hollow N-doped carbon (CoRu-O/A@HNC) derived from Ru-doped hollow MOF precursor via a two-step thermal conversion process. [174] The low content Ru (1.28%) doping can generate multiple active sites and induce Ru surface-enrichment with abundant oxygen vacancies. CoRu-O/A@HNC offers overpotential/cell voltage of 234 mV, 85 mV, and 1.558 V to reach 10 mA cm −2 for OER, HER, and overall water splitting in 1 m KOH, respectively.…”