<p>The Pt–Pd–Co system holds significant promise for application in catalytic materials for fuel cells, and the development of alloy phase diagrams provides critical guidance for synthesizing high-performance catalysts. However, there is a paucity of research on such phase diagrams, particularly concerning the construction of ternary-system phase diagrams. This study conducts experimental research on the phase equilibria of ternary precious metal alloys within the Pt–Pd–Co system. It was observed that the Pt₇Pd₂₀Co₇₃ alloy exhibits two phases, while the Pt₂₅Pd₂₀Co₅₅ alloy exhibits three phases at 400℃. Additionally, thermodynamic models of the ternary system were established, and the thermodynamic parameters were optimized using the CALPHAD method. The phase diagram obtained through optimization calculations showed good agreement with the experimental results.</p> Graphical Abstract <p>Optimized isothermal sections for the Pt–Pd–Co alloy. The black square represents two experimental points.</p> <p></p>