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Development of excellent bi-functional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) remains a key issue for the commercialization of various electrochemical devices such as fuel cells and metal-air batteries. Herein, we report the synthesis and electrocatalytic performance of mesoporous nanostructured spinel-type MFe 2 O 4 (M = Co, Mn, Ni) oxides which can serve as alternative low-cost bi-functional electrocatalysts for ORR/OER. Loaded on XC-72 carbon support, the MFe 2 O 4 spinel oxides show the M-dependent catalytic activities with CoFe 2 O 4 being the most active electrocatalyst followed by MnFe 2 O 4 and NiFe 2 O 4 for ORR. For the OER, however, the activity increases in the order: MnFe 2 O 4 < NiFe 2 O 4 ≈ CoFe 2 O 4 . Additionally, the CoFe 2 O 4 catalyst shows the smallest overpotential between ORR and OER. Compared with commercial IrO 2 , the MFe 2 O 4 catalysts reveal comparable OER activities. Furthermore, the MFe 2 O 4 catalysts exhibit much better methanol tolerance and stability than Pt/C. Meanwhile, both electrochemical measurements and density functional theory (DFT) calculations verify that the ORRs on the MFe 2 O 4 catalysts are a direct 4 e − pathway in the alkaline solution, and expound the reason for the excellent methanol tolerance of MFe 2 O 4 . [ABSTRACT FROM AUTHOR]

Oxygen reduction reaction (ORR) is of crucial importance in fuel cells and metal–air batteries, however, the sluggish dynamics of ORR remains a critical issue to be addressed. Here, we report the preparation of hexagonal spinel-type Mn 2 AlO 4 nanosheets with a high BET surface area of up to 164 m 2 g −1 through a dealloying–annealing strategy. The Mn 2 AlO 4 catalyst shows a good catalytic activity towards ORR in the alkaline solution, as well as much better methanol tolerance than the commercial Pt/C. Moreover, both the electrochemical measurements and density functional theory (DFT) calculations (adsorption energy, density of states, H 2 O 2 decomposition) demonstrate that the ORR on Mn 2 AlO 4 is a four-electron pathway. In addition, the DFT results expound the reason why the Mn 2 AlO 4 catalyst has much better methanol tolerance than Pt/C. [ABSTRACT FROM AUTHOR]

Coralloid-Pt nanodendrites decorated nanoporous gold films (NPG-Ptx) were fabricated through underpotential deposition/in-situ reduction replacement (UPD/IRR) strategy and exhibit significantly enhanced ORR activities. Ab initio density functional theory (DFT) studies further demonstrate the ORR mechanism of NPG-Ptx. [Display omitted] • Coralloid-Pt nanodendrites decorated nanoporous gold films (NPG-Ptx) were fabricated through underpotential deposition/in-situ reduction replacement (UPD/IRR) strategy. • The NPG-Ptx (x = 1 ∼ 4) exhibit significantly enhanced ORR activities in acidic media. • The DFT studies demonstrate the ORR mechanism and rate-determining step of NPG-Ptx follow the free energy diagrams. • The PDOS results indicate a relatively stronger O 2 reaction capacity on Pt side than Pt top. Deposition of trace amounts of Pt onto nanoporous gold ligaments (NPG-Pt) has demonstrated promising performance of low-Pt electrocatalysts for oxygen reduction reaction (ORR); however, improving the activity of ORR remains challenging because of the difficulty in understanding the electronic effect between Pt and NPG as well as the absence of ORR mechanism studies on NPG-Pt. Here we show that NPG-Ptx (x = 1 ∼ 4), unique coralloid-Pt nanodendrites decorated nanoporous gold films through underpotential deposition/in-situ reduction replacement (UPD/IRR) strategy, exhibit significantly enhanced ORR activities. Among them, NPG-Pt3 exhibits the best ORR activity compared with the others and Pt/C in acidic media. Density functional theory (DFT) studies demonstrate the ORR mechanism and rate-determining step of NPG-Ptx follow the free energy diagrams. Furthermore, the projected density of state (PDOS) results reveal a relatively weaker O 2 reaction capacity on the top side of Pt (Pt top) than the side site (Pt side) for NPG-Ptx. The increase of d -band center for NPG-Ptx pushes up the energy of the antibonding state above the Fermi level, and then the backflow of electrons into the system makes the energy more stable, optimizing the ORR activity. These results provide new inspirations for the development of low-Pt electrocatalysts for energy technologies in a rational manner. [ABSTRACT FROM AUTHOR]

Advancing the development of economical, high-performance, and durable non-precious metal electrocatalysts for oxygen evolution reaction (OER) holds critical significance. This study presents a self-supporting ternary metal phosphide (NiCoFe–P/NF) electrode developed by direct phosphating metal-organic frameworks (MOFs) precursor. Benefiting from a three-dimensional hierarchical porous structure, optimized electronic configuration, high electrical conductivity, and synergistic effect of multiple elements, the synthesized NiCoFe–P/NF electrocatalyst exhibits exceptional catalytic performance compared to the monometallic or bimetallic phosphides, achieving a low overpotential of 209 mV and a Tafel slope of 29 mV dec−1 at 10 mA cm−2 in 1 M KOH solution. In addition, the prepared catalyst exhibits superior stability and durability, as evidenced by its well-preserved morphology after 48 h of stability test. Furthermore, at a high current density of 100 mA cm−2, the long-term efficiency remains >90% even after 96 h. Density functional theory (DFT) calculations reveal that the high catalytic performance of the NiCoFe–P/NF catalyst is ascribed to modified electronic states and lower adsorption energy to the related species. This study not only presents the synthesis of extremely stable and active OER catalysts but also offers a novel and practical method for the development of new catalysts. [Display omitted] • Self-supporting trimetallic phosphide was investigated for OER. • NiCoFe–P/NF electrode provides superior OER activity and stability. • DFT calculations explain the origin of the high catalytic activity. • A chemically uniform trimetallic two-dimensional MOF served as the precursor. [ABSTRACT FROM AUTHOR]

Given its superior structure, the abundance of surface functional groups, and low cost, cotton fiber filtration paper can be used as the support for hydrogen evolution reaction (HER) and oxygen evolution reaction catalysts (OER) instead of copper foam (CF), nickel foam (NF), or carbon cloth (CC). Herein, the chemical plating method was used to create thin self-supporting electrodes based on cotton fiber filtration paper (FP). The Co-Ni-P amorphous nanospheres can be uniformly dispersed on the self-supporting FP due to its porous structure and oxygen functional groups. The Co-Ni-P/FP electrode has an overpotential as low as 125 mV for HER and 320 mV for OER at the current density of 10 mA cm−2. Additionally, according to density functional theory (DFT) calculations, the Co atom added to the Ni-P nanosphere can lead to considerably more charge accumulation around the Co and Ni active sites, which greatly encourages the HER and OER processes. The novel porous support, FP, provides a fresh way the preparation of self-supporting electrodes. [Display omitted] • Filter paper is used to prepare the self-supporting electrode as the substrate. • The preparation method is simple and the properties are stable. • Rich oxygen-containing functional groups of FP promote deposition and dispersion. • Explore the excellent electrochemical performance of amorphous Co-Ni-P/FP by DFT. [ABSTRACT FROM AUTHOR]

• Co 3 V 2 O 8 -T (T = temperature/°C) are prepared as bifunctional electrocatalysts. • Co 3 V 2 O 8 -400 nanofibers show small Tafel slopes of 43 and 63 mV dec−1 for ORR and OER. • The Co 3 V 2 O 8 -400 nanofiber has the best catalytic activities for ORR and OER. • The mechanism of Co 3 V 2 O 8 -400 nanofiber is simulated by DFT. Highly active and stable bifunctional electrocatalysts towards oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are necessary for practical fuel cells, metal-air batteries, and water splitting. Herein, we report a series of bifunctional Co 3 V 2 O 8 -T (T = temperature/°C) electrocatalysts by using Co-carbon electrospun nanofiber as a template, followed by a one-step calcination process. As expected, the developed Co 3 V 2 O 8 -400 nanofiber electrocatalyst shows a very small Tafel slope of 43 and 63 mV dec−1 for the ORR and OER in the alkaline solution, respectively. In addition, density functional theory (DFT) calculations reveal that the metallic conductivity and interface V-Co interaction of Co 3 V 2 O 8 -400 nanofiber boost ORR and OER electrocatalytic reactions. [ABSTRACT FROM AUTHOR]