The world's growing energy demand and the necessity of protecting the environment motivate researchers and industry alike to look for an ecological alternative to fossil fuels as energy sources and carriers, such as hydrogen. On the other hand, biomass waste can be used to obtain bio-oil for energy applications. Fast pyrolysis of biomass results in the highest bio-oil yields, but poor physicochemical properties characterise the produced biochar. This work aimed to develop a procedure to make an electrocatalyst of the oxygen evolution reaction (OER) to produce hydrogen based on biochar from fast pyrolysis of renewable raw materials (carbonised triticale straw, sunflower husk, pine sawdust, walnut shells, and sewage sludge) with a cobalt active phase. No additional chemical and thermal valorisation was applied to increase the graphitisation degree, porosity and specific surface area. However, simple and environmentally friendly air plasma was used as a non-destructive method to improve the surface properties of the biochar materials. The cobalt active phase was introduced by a deposition-precipitation method. The surface modification of carbon materials with plasma improves the electrocatalytic activity by changing the speciation of the biochars' surface oxygen groups. The activity of the obtained materials is very similar, irrespective of the different characteristics of the studied fast pyrolysis by-products, indicating that the developed materials can be obtained from various biochars. The OER overpotentials at for all the samples are below 385 mV. The most active material, based on plasma-treated triticale straw biochar , demonstrated the lowest overpotential of 358 mV, representing a slight improvement compared to its untreated counterpart (η = 363 mV). Furthermore, the catalyst maintained stable operation for 6 h at a current density of , in contrast to the reference cobalt spinel, which operated for only 3 h at a current density of . These findings underscore the potential of plasma-functionalised waste-derived biochars as sustainable and effective catalysts for OER applications.