We report for the first time effects of altering the amount of Pd supported on high-surface area carbon (Pd/C). Cyclic voltammetry in 0.1 M H2SO4 using Pd/C electrocatalysts with distinct metal-to-carbon ratio, Pd black and a Pd wire electrodes reveals unambiguously metal loading effects, such as a decrease in the peak potential for the reduction of palladium oxide (PdO), an increase of the charges of desorption of hydrogen, and formation/ reduction of PdO with the Pd content. Such effects need to be taken into account when designing Pd-based Fuel Cells electrocatalysts. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.