In Situ Exploring of the Origin of the Enhanced Oxygen Evolution Reaction Efficiency of Metal(Co/Fe)–Organic Framework Catalysts Via Postprocessing

Abstract

The oxygen evolution reaction (OER) is of vital importance for electrochemical energy conversion technologies. The use of metal−organic framework (MOF) catalysts after postprocessing is an important method to optimize catalytic activity; however, little attention has been paid to the transformation of the electronic structure and coordinated ions under operando conditions. Here, we focus on a Prussian blue analogue (PBA) with the formula Na 2 Co 2+ [Fe 2+ (CN) 6 ]•nH 2 O after postprocessing at a temperature of 400 °C. The catalysts exhibit a significant improvement in the OER activity with an overpotential of 254 mV against 320 mV for the initial PBA at 10 mA cm −2 in 1 M KOH. Our ex situ soft X-ray absorption spectroscopy (XAS) results demonstrate that some of the high-spin Co 2+ and low-spin Fe 2+ ions of PBA exhibit exchange with N and C ligands. Our fast operando hard XAS study revealed a dynamic evolution process of the transformation of ligands from N(C) in the initial Na 2 Co[Fe(CN) 6 ]•nH 2 O to oxygen and the formation of pure low-spin Co 3+ oxide and high-spin Fe 3+ oxide after OER. The amorphous (Co,Fe)OOH chemical state was identified as the catalytically active state based on our operando X-ray spectroscopy results. The results of this study provide insights into a dynamic evolution process of MOFs after postprocessing and the formation of real active sites during electrocatalysis.

Simultaneous optimization of CoIr alloy nanoparticles and 2D graphitic-N doped carbon support in CoIr@CN by Ir doping for enhanced oxygen and hydrogen evolution reactions

“…Normally, the overall efficiency of water splitting always suffers from high overpotential and sluggish kinetics of the OER and HER, particularly the anodic OER with a four proton-coupled electron transfer process. [3][4][5][6] Therefore, developing high performance bifunctional catalysts for OER and HER with low electrochemical overpotentials remains a signicant challenge to realize continual water splitting for real applications. Iridium (Ir), ruthenium (Ru) and their oxides are considered as benchmark OER electrocatalysts that exhibit reasonably high activity, while platinum (Pt)-based materials are identied as the most efficient HER catalysts.…”

“…Normally, the overall efficiency of water splitting always suffers from high overpotential and sluggish kinetics of the OER and HER, particularly the anodic OER with a four proton-coupled electron transfer process. 3–6 Therefore, developing high performance bifunctional catalysts for OER and HER with low electrochemical overpotentials remains a significant challenge to realize continual water splitting for real applications.…”

Construction of Ni‐Co‐Fe Hydr(oxy)oxide@Ni‐Co Layered Double Hydroxide Yolk‐Shelled Microrods for Enhanced Oxygen Evolution

“…Iron (Fe) hydr(oxy)oxides have gained considerable attention owing to their abundant reserves and promising activity for OER [13] . However, the OER performance of Fe‐based electrocatalysts is still far from satisfactory, which is restricted by the poor intrinsic activity and dissolution of active Fe species during the stability test [14–16] .…”

Regulating the coordination environment of a metal–organic framework for an efficient electrocatalytic oxygen evolution reaction

“…51 In terms of microstructure design, doping heterogeneous metal atoms and different ligands into the crystal lattice can improve the electronic structure. 52–54 The latter is more challenging, 55 and the electrocatalytic performance of MOFs needs to be enhanced to the next level. 56…”

“…51 In terms of microstructure design, doping heterogeneous metal atoms and different ligands into the crystal lattice can improve the electronic structure. [52][53][54] The latter is more challenging, 55 and the electrocatalytic performance of MOFs needs to be enhanced to the next level. 56 To deal with the above challenges, we have synthesized a bimetal-organic framework (FeCo-L 1 L 2 ) using a simple and cost-effective solvothermal method using the free assembly of Fe and Co ions with 2,5-dihydroxyterephthalic acid (defined as L 1 ) and 4,6-dihydroxyisophthalic acid (defined as L 2 ).…”