Binder-free Ruthenium Embedded Carbon fiber Electrodes for Electrocatalytic Hydrogen Generation From water

Abstract

1. Introduction

Since the 1860s, carbon fibers (CFs) have been a major contribution to various industries [1]. CFs can be used as active electrochemical electrodes as it offers high mechanical properties, low density, and good electroconductivity, strong resistivity of general corrosion, and chemical attack. However, carbon-supported metal composite has not been realized as a practical fabric electrocatalyst (FEC) electrode due to the metal dissolution and aggregation problems caused by unstable adhesion between the metal and carbon fiber [2]. To rectify the stability issue, binders must be applied, which inevitably reduces the catalytic active surface [3, 4]. In this study, a method has been devised to manufacture the binder-free fabric electrodes using mass-producible wet spinning. Besides, the internal structure of fibers intertwined with metal was investigated to elucidate the relationship between catalytic activity and structure.

2. Experimental

In order to achieve highly efficient water-splitting for generating hydrogen (H2) as clean energy electrochemical reaction, ruthenium (Ru) was selected as a metal catalyst that possesses a similar bond strength with hydrogen (~65 kcal mol-1) to platinum (Pt). Ru-anchored fiber electrocatalyst (Ru-FEC) was prepared by the wet-spinning technique (Fig. 1). The nitrile group in polyacrylonitrile (PAN) supported that Ru ions are stably anchored on precursor fiber. To optimize the electrocatalytic activity of the Ru-FEC, oxygen (O2) plasma treatment was employed to increase the exposure of Ru to the surface by removing carbon. The morphology, composition, changes in carbon and Ru structure according to the heat treatment temperature of the as-prepared Ru-FEC were characterized by XRD, FE-SEM, HR-TEM, TGA. The electrochemical HER activity and stability of the Ru-FEC were evaluated using a typical three-electrode system in a N2-saturated 1.0 M KOH solution.

3. Results and Discussion

As the temperature increases, the development of the graphitic structure, and Ru shows that the crystal grows and becomes clear from 1200 °C and it appears that aggregation takes place at around 1400 °C. Between 1000 and 1200 °C, ultrafine Ru nanoparticles were observed with a diameter of less than 10 nm in all with a diameter of around 5 nm providing a high density of active sites at a specific area. From linear sweep voltammogram (LSV), the Tafel slope was calculated from the results of 1000 to 1300 °C, showing the electrochemical kinetics of 233.0, 112.6, 86.6, and 101.4 mV dec-1 respectively. The Ru-FEC 1200 °C shows the highest activity among other temperature ranges at an overpotential of under 20 mV.

4. Conclusions

Continuous, neat, PAN-based Ru anchored carbon fiber was prepared by wet spinning method. In-situ reduction of Ru precursor was employed and the carbonization of polymeric fiber was conducted by heat treatment, showing the outstanding stability in hydrogen evolution reaction. The structure evolution of carbon and metal nanoparticles were observed as a function of heat treatment temperature, and the relationship between the catalytic activity of fibers and the structure was studied. The flexible and lightweight carbon fiber as an electrochemical catalyst may offer insight into processing novel fibrous electrode for various electrochemical applications.