Layered nickelates, Ln2NiO4+δ, are promising electrode materials for many electrochemical applications, including solid oxide fuel cells and electrolysis cells. Although Ln2NiO4+δ has been extensively modified by various doping strategies to tune its functional properties, the partial substitution of Ln3+ with Ba2+ remains among the least studied routes. At the same time, such substitution is found to be favorable when Ln2NiO4+δ materials are used for protonic ceramic electrochemical cells based on Ba-containing proton-conducting electrolytes (i.e., BaCeO3, BaZrO3, Ba(Ce,Zr)O3). In this work, which is the third part of a systematic study, Pr2–xBaxNiO4+δ materials are used as electrodes for a proton ceramic fuel cell and as oxygen permeable membranes. The oxygen permeation experiments confirm that the compositions with x = 0.2 and 0.3 prevail over x = 0 and 0.1 in terms of their oxygen-ionic conductivity, while the electrochemical cell characterizations confirm the high electrochemical activity of the Pr1.8Ba0.2NiO4+δ electrode in both fuel-cell- and electrolysis-cell modes. Our research thus confirms that a Ba-doping strategy is highly promising for designing new Ln2NiO4+δ-based phases, simultaneously offering good chemical and thermal compatibility with state-of-the-art proton-conducting electrolytes and high electrochemical performance.