A review on process routes and inter-process coupling mechanisms of metallic bipolar plates for fuel cells

Metallic bipolar plates are critical components of PEMFCs, and their manufacturing involves a strongly coupled process chain comprising substrate selection, coating, forming, and joining. This review systematically analyzes the coupling mechanisms among these processes and reveals how substrate choice and coating sequence fundamentally determine subsequent process windows. Two representative routes are compared: the bipolar plate route and the cell route. The substrate imposes primary constraints on coating compatibility and forming limits. The coating sequence acts as the fundamental branching point: post-coating enables high-performance coatings without forming damage but relies on expensive vacuum deposition, while pre-coating enables low-cost roll-to-roll production at the expense of coating damage during forming. The evolution from the first-to second-generation Toyota Mirai illustrates how technological maturity shifts the performance-cost trade-off. Emerging non-vacuum coating technologies are discussed as potential disruptors. This review provides a holistic framework emphasizing that there is no universal solution but only scenario-matching trade-offs.