Search

In water splitting, anode catalysts for the oxygen evolution reaction (OER), which is the rate‐determining step, are more critical than cathode catalysts. Herein, the authors prepare Ni‐IrOx composite catalysts consisting of NiO and IrO2 for the OER by a solid‐state reaction with different ratios of NiO to IrO2 and reaction temperatures. In particular, Ni‐IrOx‐400 with a molar ratio of NiO/IrO2 = 1:1 heated at 400 °C shows the best OER performance. In the overall water splitting test using an anion exchange membrane (AEM) water electrolyzer, the single cell with Ni‐IrOx‐400 as the anode catalyst shows current densities of 1454.8 mA cm−2, respectively, measured at 1.8 V. Furthermore, the stability tests of the AEM single cells are carried out at 50 °C under a constant current density of 500 mA cm−2. The single cell with Ni‐IrOx‐400 shows only a slight increase in the overpotential (rate: 2.0 mV h−1) for 100 h owing to the enhanced stability of Ni‐IrOx‐400 compared to IrO2 (12.5 mV h−1). The improved OER performance of the Ni‐IrOx‐400 may be attributed to a composite structure that can prevent particle agglomeration and thus preserve the active sites during the OER. [ABSTRACT FROM AUTHOR]

Doped carbon structures have been developed as non-precious metal catalysts for oxygen reduction reactions (ORR) in polymer electrolyte membrane fuel cells (PEMFCs). Among doped carbon structures, Fe- and N-doped carbon (Fe/N/C) nanostructured catalysts have received attention due to their catalytic activity, comparable to that of Pt, avoiding the use of critical raw materials. However, obviously, its durability is not yet neither fully understood nor comparable to that of traditional catalysts. In this study, we synthesized mesoporous F-doped Fe/N/C, which is a tri-doped carbon nanostructure, as a cathode catalyst for ORR. Tri-doped carbon catalysts with different amounts (x) of F (Fx-Fe/N/C) were prepared using Fe-5,10,15,20-tetrakis(4-methoxyphenyl)-21H,23H-porphine iron(III) chloride and NH 4 F as the Fe/N- and F- doping sources, respectively, and Santa Barbara amorphous-15 as the template. Fx-Fe/N/C with an optimal F content exhibited excellent electrocatalytic performance for ORRs i.e. a high half-wave potential of 809 mV in 0.1 M HClO 4 solution, a maximum power density of 280 mW cm−2, and a high stability for 4000 min at 0.5 V, owing to the high proportion of FeN x and pyridinic N as active sites, strong C–F bonds, and hydrophobic surfaces. We synthesized mesoporous F-doped Fe/N/C, which is a tri-doped carbon nanostructure, as a cathode catalyst for ORR. Fx-Fe/N/C with an optimal F content exhibited excellent electrocatalytic activity and durability for ORRs owing to the high proportion of FeNx and pyridinic N as active sites, strong C–F bonds, and hydrophobic surfaces. [Display omitted] [ABSTRACT FROM AUTHOR]

For a high-performance OER, we synthesized NiFe LDH as an anode catalyst with a high specific surface area and electrical conductivity using a solvent ratio-adjusted hydrothermal method. [Display omitted] • We synthesized NiFe LDH using a solvent ratio-adjusted hydrothermal method. • The oxygen vacancies produced by alcoholysis promote the charge transfer rate. • The interplanar distance was increased by inserting nitrate in NiFe LDH. • WE 55 synthesized at a proper ratio of water and ethanol showed the best performance. NiFe layered double hydroxides (LDH) with their high specific surface areas have been used as alternatives to noble metal catalysts for the oxygen evolution reaction (OER) in anion exchange membrane water electrolysis. However, for bulk LDH structures, relatively narrow interplanar distances can lead to the slow diffusion of OH− and the induction a local acidic atmosphere, resulting in catalyst corrosion. In this study, we synthesize solvent (water and ethanol) ratio-adjusted NiFe LDH anode catalysts to enhanced the OER. Results show that the catalyst prepared at a 5:5 ratio of water and ethanol (WE 55) delivers a low overpotential of 310 mV at 50 mA cm−2, Tafel slope of 40.5 mV dec−1, and 100 h-stability in a half-cell test, and a high current density of 744.2 mA cm−2 at 1.8 V and 70 °C in a single-cell test. WE 55 exhibits a manipulated oxygen vacancy and a substantially high specific surface area of ∼ 164.5 m2 g−1, leading to improved charge transfer and mass transport rates. [ABSTRACT FROM AUTHOR]

Anion exchange membrane water electrolysis (AEMWE) uses a zero-gap membrane-electrode-assembly (MEA) consisting of a polymer electrolyte membrane and non-precious metal-based catalysts. However, anode catalysts for the oxygen evolution reaction (OER), which is the rate-determining-step in WE, need to be intensively developed to achieve superior electrocatalytic activity and stability. Herein, we report the synthesis and characterization (experimental and simulation) of spherical Ni-doped (5–15 at%) cobalt phosphide (Ni-CoP) as the anode catalyst for the OER. Specifically, the DFT calculation exhibited that the addition of Ni in CoP might increase the energy density in the Fermi level of pristine CoP, enhance the charge transfer rate during the OER, and reduce the energy barrier for the formation of OOH* , thereby boosting the OER activity. The prepared Ni-doped CoP catalyst was directly loaded onto a foam-type Ni-based gas diffusion layer for effective application in AEMWE. It was found that the electrocatalytic activity of the AEMWE depends on the porosity of the NFs as catalyst substrates. The unit cell containing the membrane-electrode-assembly fabricated with NCP-10 delivered a high current density of 1.12 A cm−2 at 1.8 V and a low reduction rate of 0.64 mA cm−2 h−1 for 250 h. [Display omitted] • Spherical Ni-doped CoP (NCP) was prepared as the anode catalyst for the OER. • The prepared NCP catalyst was loaded onto a Ni-foam (NF) in AEMWE. • The electrocatalytic activity of the AEMWE depends on the porosity of the NFs. • CoP doped with 10 at% Ni (NCP-10) exhibited improved OER performance. • The AEMWE fabricated with NCP-10 delivered enhanced performance. [ABSTRACT FROM AUTHOR]

Water electrolysis (WE) is an attractive advanced technology for the production of H 2. A key issue in the WE is to develop suitable catalysts for the oxygen evolution reaction (OER), where a relatively large energy loss occurs. The Ir-doped NiCo 2 O 4 catalysts exhibit the formation of a solid solution and a porous nanostructure. The oxygen vacancies formed by Ir doping can enhance the electrocatalytic activity for the OER owing to increased electrical conductivity and tunable adsorption energies of OH- and H 2 O. In comparison to IrO 2 as a representative OER catalyst, the Ir(10 at%) doped NiCo 2 O 4 catalyst (10-Ir-NCO) exhibits the better OER performance (overpotential of 303 mV at 10 mA cm−2) and its stability for 20,000 s. In addition, in the overall water splitting test, the 10-Ir-NCO || Pt/C exhibits the excellent OER activity (a low overpotential of 0.5 V at 100 mA cm−2) and stability (20 h at 50 mA cm−2). [Display omitted] • Ir-doped NiCo 2 O 4 catalysts were synthesized with various amounts of Ir dopant. • The catalysts exhibited a spinel structure consisting of NiCo 2 O 4 host and Ir dopant. • The catalyst exhibited the enhanced activity and stability for the OER compared to IrO 2. • The enhanced activity may result from the replacement of Ni and Co with Ir in octahedral sites. • The enhanced activity may be attributed to the oxygen vacancies. [ABSTRACT FROM AUTHOR]