Hollow nickel ferrite nanofibers templated using waste expanded polystyrene as electrocatalysts of the hydrogen evolution reaction

Abstract

The electrochemical hydrogen evolution reaction is a process of central importance to a future hydrogen economy and the de-fossilization of various industrial processes. To operate with high efficiency, electrocatalysts are required for this reaction, of which Pt is the best known to date. However, due to its scarcity and the ongoing environmental cost of mining precious metals, the development of alternatives based on first row transition metals is an area of very intense interest. Whilst the performance of such earth-abundant catalysts cannot compete with Pt on an atom-for-atom basis, engineering the morphology of first row transition metal catalysts can produce significant improvements in performance relative to the bulk solids. Herein, we highlight one such example, whereby multichannel carbon nanofibers (formed using waste polystyrene as a key component) were used to template the formation of hollow NiFe 2 O 4 nanofibers with a surface area (167 m²/g), which was nearly double that of pristine NiFe 2 O 4 (81 m²/g). The material was thoroughly characterized by a range of methods and was found to exhibit significantly enhanced activity for the hydrogen evolution reaction: in linear sweep voltammetry, the porous hollow NiFe 2 O 4 nanofibers required an overpotential of 178 ± 3 mV to deliver a current density of 50 mA cm -2 , compared to 342 ± 2 mV for the pristine NiFe 2 O 4 material. The results showcase the advantages of morphological control of catalysts for improving hydrogen evolution activity.