Graphene-based materials and their role in electrocatalysis related to hydrogen production have been intensively investigated by many authors, often justified through a low price of such materials. In this study we used single-step electrodeposition/graphene oxide reduction route to prepare Ni@reduced-graphene-oxide composites for electrochemical hydrogen evolution reaction (HER). As the precursors for reduced graphene oxide, two different home-made graphene oxides were used. When compared to pure electrodeposited Ni, composite catalysts show improved catalytic activity which depends on Ni electrodeposition time in a volcano-type fashion. Using electrochemically prepared graphene oxide, HER overvoltage needed to reach 10 mA cm −2 was reduced to only −97 mV, showing the improvement by roughly 200 mV when compared to pure electrodeposited Ni. It was concluded that structural disorder and surface oxidation of graphene-based materials are the key properties for reaching high HER activities of such prepared catalysts. Based on this observation, it was discussed whether it is economically justified to use high quality graphene oxide for the preparation of HER catalysts, as the price (production and commercial) of this material can be extremely high, often exceeding the price of platinum.

The increasing energy demands of modern society require a deep understanding of the properties of energy storage materials, as well as the tuning of their performance. We show that the capacitance of graphene oxide (GO) can be precisely tuned using a simple electrochemical reduction route. In situ resistance measurements, in combination with cyclic voltammetry measurements and Raman spectroscopy, have shown that upon reduction GO is irreversibly deoxygenated, which is further accompanied by structural ordering and an increase in electrical conductivity. The capacitance is maximized when the concentration of oxygen functional groups is properly balanced with the conductivity. Any further reduction and deoxygenation leads to a gradual loss of capacitance. The observed trend is independent of the preparation route and the exact chemical and structural properties of GO. It is proposed that an improvement in the capacitive properties of any GO can be achieved by optimization of its reduction conditions.

1 Department of chemistry, Faculty of Science, Zmaja od Bosne 33-35, Sarajevo, Bosnia and Hercegovina 2 University of Belgrade Faculty of Physical Chemistry, Studentski trg 12-16, 11158 Belgrade, Serbia 3 Laboratory for Micro and Nanotechnology, Paul Scherrer Institute, Villigen, Switzerland. 4 Serbian Academy of Sciences and Arts, Knez Mihajlova 35, 11000 Belgrade, Serbia * E-mail: slavko@ffh.bg.ac.rs