Stable CuO with variable valence states cooperated with active Co2+ as catalyst/co-catalyst for oxygen reduction/methanol oxidation reactions

ZIF67-ZIF8@MFC-Derived Co-Zn/NC Interconnected Frameworks Combined with Perfluorosulfonic Acid Polymer as a Highly Efficient and Stable Composite Electrocatalyst for Oxygen Reduction Reactions

The development of precious metal-free (M-N-C) catalysts for the oxygen reduction reaction (ORR) is considered crucial for reducing fuel cell costs. Herein, Co-Zn/NC interconnected frameworks with uniformly dispersed Co nanoparticles and graphitic carbon are designed and successfully synthesized through the in situ growth of zeolitic imidazolate frameworks (ZIF67 and ZIF8) along with biomass nano-microfibrillar cellulose (MFC), followed by pyrolysis. A Co-Zn/NC composite is prepared by combining Co-Zn/NC with a perfluorosulfonic acid polymer. The Co-Zn/NC composite catalyst exhibits excellent ORR catalytic activity (E0 = 0.974 V vs. RHE, E1/2 = 0.858 V vs. RHE) and good long-term durability, with 90% current retention after 10000s, surpassing that of commercial Pt/C in alkaline media. The hierarchical porous structure, coupled with the uniform distribution of Co nanoparticles and nitrogen doping, contributes to superior electrocatalytic performance, while the interconnected frameworks and graphitic carbon ensure good stability. Additionally, the Co-Zn/NC composite demonstrates promising applications in acidic media. This strategy offers significant guidance to develop advanced non-precious metal carbon-based catalysts for highly efficient and stable ORR.

Thermally Methanol Oxidation via the Mn1@Co3O4(111) Facet: Non-CO Reaction Pathway

Co3O4, as the support of single-atom catalysts, is effective in electron-structure modulation to get distinct methanol adsorption behaviors and adjustable reaction pathways for the methanol oxidation reaction. Herein, we considered the facets that constitute a Co vacancy of the Co3O4(111) facet and a foreign metal atom M (M = Fe, Ni, Cu, Ru, Rh, Pd, Ag, Os, Ir, Pt, Au, Mn) leading to single-atom catalysts. The Mn1@Co3O4(111) facet is the facet considered the most favorable among all of the possible terminations. Oxygen adsorption, decomposition, and its co-adsorption with methanol are the vital steps of methanol oxidation at the exposed Mn1@Co3O4(111) facet, giving rise to the stable configuration: two O* and one CH3OH* adsorbates. Then, the Mn1@Co3O4(111) facet activates the O-H and C-H bonds within CH3OH*, advances CH3O* → H2CO* → HCOO* → COO*, and releases the products H2, H2O, and CO2 consecutively.

Low-Pt Octahedral PtCuCo Nanoalloys: "One Stone, Four Birds" for Oxygen Reduction and Methanol Oxidation Reactions

To find a low-Pt electrocatalyst that is functionally integrated and superior to the state-of-the-art single-Pt electrocatalyst is expectedly a challenge. We have in this study found that the reactivity of the oxygen reduction reaction (ORR) and the methanol oxidation reaction (MOR), in both acidic and alkaline electrolytes (viz., four half-cell reactions), can be modified and greatly enhanced by the electronic and/or synergistic effects of a low-Pt octahedral PtCuCo alloy. For the ORR, the mass activity (MA) of Pt_0.23Cu_0.64Co_0.13/C in an acidic or alkaline electrolyte was 14.3 or 10.7 times that of the commercial Pt/C. For the MOR, the MA of Pt_0.23Cu_0.64Co_0.13/C in an acidic or alkaline electrolyte was 7.2 or 3.4 times that of the commercial Pt/C. In addition, Pt_0.23Cu_0.64Co_0.13/C exhibited an increased durability and CO tolerance, as compared with the commercial Pt/C. Density functional theory calculations demonstrated that the PtCuCo(111) surface can effectively optimize the O* binding energy. This work has successfully shown an example of how both acidic and alkaline ORR and MOR activities can be significantly synchronously enhanced.

NaCl sealing Strategy-Assisted synthesis CoO-Co heterojunctions as efficient oxygen electrocatalysts for Zn air batteries

Developing highly efficient, low-cost, and stable bifunctional oxygen electrocatalysts is essential for the wide popularization of rechargeable Zn-air batteries. Combining zero-dimensional metal nanoparticles with two-dimensional metal oxide nanosheets is an appealing strategy to balance performance and cost. However, the precise construction of these composites remains a great challenge, and their interaction mechanisms lack thorough study. Herein, a cobalt-oxide-based bifunctional oxygen electrocatalyst comprising a rich Co-CoO heterointerface (CoO/Co@NG) was synthesized via a NaCl sealing-assisted pyrolysis strategy. The NaCl crystals played the role of a closed nanoreactor, which facilitated the formation of a CoO-Co heterojunction. Experimental results and theoretical calculations confirmed that the ingeniously constructed heterojunction expedited the oxygen reduction reaction and oxygen evolution reaction kinetics, which is superior to Pt/C. When serving as the air electrode in an assembled liquid-state Zn-air battery, the battery shows high power density (215 mW cm^-2), specific capacity (710 mAh g_zn^-1), and outstanding durability (720 h at 10 mA cm^-2). This work provides an innovative avenue to design high-performance heterojunction electrocatalysts for perdurable Zn-air batteries.

Pt-Co Electrocatalysts: Syntheses, Morphologies, and Applications

Pt-Co electrocatalysts have attracted significant attention because of their excellent performance in many electrochemical reactions. This review focuses on Pt-Co electrocatalysts designed and prepared for electrocatalytic applications. First, the various synthetic methods and synthesis mechanisms are systematically summarized; typical examples and core synthesis parameters are discussed for regulating the morphology and structure. Then, starting with the design and structure-activity relationship of catalysts, the research progress of the morphologies and structures of Pt-Co electrocatalysts obtained based on various strategies, the structure-activity relationship between them, and their properties are summarized. In addition, the important electrocatalytic applications and mechanisms of Pt-Co catalysts, including electrocatalytic oxidation/reduction and bifunctional catalytic reactions, are described and summarized, and their high catalytic activities are discussed on the basis of their mechanism and active sites. Moreover, the advanced electrochemical in situ characterization techniques are summarized, and the challenges and direction concerning the development of high-performance Pt-Co catalysts in electrocatalysis are discussed.