Abstract
Two-dimensional (2D) metal organic frameworks (MOFs) are emerging as low-cost oxygen evolution reaction (OER) electrocatalysts, however, suffering aggregation and poor operation stability. Herein, ultrafine Fe3O4 nanoparticles (diameter: 6 ± 2 nm) are homogeneously immobilized on 2D Ni based MOFs (Ni-BDC, thickness: 5 ± 1 nm) to improve the OER stability. Electronic structure modulation for enhanced catalytic activity is studied via adjusting the amount of Fe3O4 nanoparticles on Ni-BDC. The optimal Fe3O4/Ni-BDC achieves the best OER performance with an overpotential of 295 mV at 10 mA cm−2, a Tafel slope of 47.8 mV dec-1 and a considerable catalytic durability of more than 40 h (less than 5 h for Ni-BDC alone). DFT calculations confirm that the active sites for Fe3O4/Ni-BDC are mainly contributed by Fe species with a higher oxidation state, and the potential-determining step (PDS) is the formation of the adsorbed O* species, which are facilitated in the composite.
Highlights
With increasing concerns of fossil fuel related environmental crisis and global warming, there is an imperative demand for developing alternative green and sustainable energy conversion and storage technologies, such as batteries, fuel cells and water splitting [1,2,3,4,5,6,7]
Dehydroascorbic acid (DHAA) is oxidized from the ascorbic acid, serving as a stabilizer and capping ligand on surfaces of Fe3O4 nanoparticles interacted by carbonyl groups, ensuring a good dispersibility of Fe3O4 nanoparticles in aqueous solution
During the subsequent sonication process, functionalized Fe3O4 nanoparticles are homogenously dispersed in an alkaline solution, immobilized on 2D Ni-BDC
Summary
With increasing concerns of fossil fuel related environmental crisis and global warming, there is an imperative demand for developing alternative green and sustainable energy conversion and storage technologies, such as batteries, fuel cells and water splitting [1,2,3,4,5,6,7]. Avoiding aggregation with high active surface area and improving the integral structural stability for superior OER catalysts are essential To tackle these issues, there are increasing reports demonstrating that the introduction of functional nanoscale components (nanosheets or nanoparticles etc.) in a MOF composite could prevent the aggregation and enhance the integral structural stability during operation [30,31]. Qin et al have reported hybrids of Fe-Co polyphenolic network wrapped Fe3O4 nanocatalysts for enhanced OER with a η of 260 mV at 10 mA cm-2 and a durability over 24 h, taking advantage of strong metalpolyphenolic ligand complexation that ensures robust metal Co-Fe polyphenolic shells for prolonged operations [31] Inspired by these reports, 2D Ni based MOFs could be promising candidates for constructing hybrid electrocatalysts due to excellent surface structure and physicochemical features. DFT calculations are further conducted to identify the active site and help to understand how the valance state of transition metals affects the OER performance
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