Developing new low-cost high-performance cobalt-free cathode materials for low temperature proton-conducting solid oxide fuel cells (H-SOFCs) has been an imperative topic. In response to this challenge, we herein develop a novel in situ Pr diffusion strategy based on a Sm_0.2Ce_0.8O_2-δ-Pr(Pr_0.5Ba_1.5)Cu₃O_7-δ (SDC-PBCu, 3:7 wt%) compound, to achieve a perovskite-related proton-blocking composite cathode (PBCC) Ce_1-xPr_xO_2-δ-Ba₂CeCu₃O_7.4-Sm₂Ba_1.33Ce_0.67Cu₃O₉-CuO (PDC-BCC-SBCC-CuO) for BaZr_0.1Ce_0.7Y_0.2O_3-δ-based H-SOFCs. The single cell achieves a remarkable performance with a maximum power density (MPD) of 1000 and 566 mW cm^-2, corresponding to the interfacial polarization resistance (R_P) of 0.037 and 0.188 Ω cm² at 700 and 600 °C, respectively. The XRD results demonstrate that the PBCu phase disappears after the calcination of the mixed SDC-PBCu composite powder at 900 °C, with the formation of four new phases including fluorite structured PDC, orthorhombic layered material BCC, tetragonal perovskite-related SBCC and a small quantity of metallic oxide CuO, being favorable for a superior cathode performance. The ascendant electrochemical performance including the very high MPD and the lower R_P obtained here indicate that the quaternary cobalt-free PBCC PDC-BCC-SBCC-CuO is a preferable alternative for high-performance low-temperature H-SOFCs.