Electrospun Cu‐Deposited Flexible Fibers as an Efficient Oxygen Evolution Reaction Electrocatalyst

Abstract

Developing oxygen evolution reaction (OER) catalysts with high activity, long‐term durability, and at low cost remains a great challenge. Herein, we report the high activity of fibrous Cu‐based catalysts. The synthesis process is simple and scalable. Electrospinning method was selected to synthesize fibrous polymer substrates (Poly(vinylidene fluoride‐co‐hexafluoropropylene, PVdF‐HFP), which are then covered by Cu via electroless deposition. Cu‐deposited PVdF‐HFP with different microstructures having smooth and roughened surfaces were also synthesized by drop‐casting and impregnation method, respectively, to emphasize the importance of the microstructures on OER activity. The OER activity and durability were studied by linear sweep voltammetry, chronoamperometry, and Tafel slope analysis. The Cu/PVdF‐HFP fibrous catalysts exhibit significantly improved OER activity and durability compared with Cu plate as well as Cu‐deposited PVdF‐HFP with different microstructures. The unique fibrous structure provides better mass transport, diffusion, and large active surface area. In addition to the advantages of the fibrous structure, attenuated total reflection infrared (ATR‐IR) and ex situ X‐ray photoelectron spectroscopy revealed that the improved specific activity for Cu/PVdF‐HFP fiber can be attributed to the synergistic effect between Cu and Cu/PVdF‐HFP (electron transfer from Cu to PVdF‐HFP) at the Cu|PVdF‐HFP interface, which results in optimized reaction energetics for the OER.

Tuning the Polarity of a Fibrous Poly(vinylidene fluoride-co-hexafluoropropylene)-Based Support for Efficient Water Electrolysis

“…The high void volume observed for all the Cu/PVdF-HFP fibers contributes to the efficient mass transfer of reactant and product molecules. 47 …”

“…The result indicates the enhanced diffusion of the reactant and/or the product for catalysts with stretch-anneal and anneal treatments. Although the high void volume of the fibrous structure improves the mass transfer of reactant and product molecules and partial exposure of hydrophobic PVdF-HFP substrate assists the removal of the reaction product (oxygen gas) from the surface, 47 both of which cannot be the reason for the steep slope of the LSV at the large overpotential region for catalysts with stretch-anneal and anneal treatments. We here propose that the ferroelectric polarizability of PVdF-HFP effectively anchors negatively charged OH – at the vicinity of the electrode, accelerating the OH supply to the Cu active sites.…”

“…The Cu-deposited fibrous electrode was prepared by the electrospinning method reported elsewhere. 47 The electrospinning solution consisted of a THF and DMF mixture (7:3 by vol) containing 10 mg of PdCl 2 (Wako Pure Chemical) with 12 wt % of poly(vinylidene fluoride- co -hexafluoropropylene) (PVDF-HFP, average molecular weight = 400,000). Electrospinning was performed using electrospinning equipment (NANON-03, MECC Co. Ltd.) at an applied voltage of 28 kV with a feeding rate of 1 mL h –1 while rotating a drum-shaped collector along the rotating axis at 3000 rpm.…”

“… 45 , 46 In this regard, to maximize the catalytic activity of Cu, optimizing the catalyst–support interaction is essential for the rational design of highly active Cu-based OER catalysts. Although the impact of the catalyst–support interaction on the OER activity has also been suggested for Cu-based catalysts, 47 , 48 insights into tuning the catalyst–support interaction to optimize the electronic structure are still insufficient and are further explored.…”

Well-Adhered Copper Nanocubes on Electrospun Polymeric Fibers

“…Polymers have been widely used to hinder aggregation and bestow stability on metallic nanostructures [ 9 ]. Hierarchical structures of conformal metallic nanostructures—either as consolidated films or discrete particles—have been successfully immobilized on electrospun nanofibers and microfibers for a broad range of applications [ 10 , 11 ].…”