The p/n-junction in heteroatoms-doped carbon might be engineered to adjust the population of the charge carriers to perform the oxygen evolution reaction (OER) with holes in a p-type region and hydrogen evolution reaction (HER) with electrons in a n-type region. The carbons (AC) with introduced Fe, Ni and Co species of hierarchical porous structures were derived by pyrolysis of melted poly (styrenesulfonic acid-co-maleic acid) salts. The obtained materials were used as HER, OER and water splitting catalysts. Although all samples were catalytically active, their activity differed depending on the kind of metal. The most promising results were obtained on Ni-AC. An overpotential of Ni-AC to reach 10 mA cm(-2) was 259, 382 and 640 mV for HER, OER and water splitting, respectively. Mott-Schottky tests indicated that Ni-AC has p/n-type semiconductor features. While its n-type region was responsible for HER, the p-type region governed OER. A high dispersion of the nickel-based catalytic centers in the hierarchical pore system resulted in an efficient utilization of the active sites for the electron transfer processes. Besides the satisfactory performance, the advantage of the derived catalyst is in its simple synthesis from a commodity polymer. (C) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.