The assumption of a highly corrosive potential at the anode bipolar plate (BPP) and porous transport layer (PTL) in a proton exchange membrane water electrolyser (PEMWE) stack often leads to selection of expensive materials such as platinum–coated titanium. Here, we develop a physicochemical model of electrochemical potential distribution in a PTL and validate it by in situ and ex situ electrochemical potential measurement. Model predictions suggest that, under typical PEMWE operating conditions, the corrosive zone associated with the anode polarisation extends only ≈200 μm into the PTL from the catalyst layer, obviating the need for highly corrosion-resistant materials through the bulk of the PTL and at the BPP. Guided by this observation, we present single cell PEMWE tests using anode current collectors fabricated from carbon-coated 316L stainless steel. The material is shown to be tolerant to potentials up to 1.2 V vs. RHE and when tested in situ for 30 days at 2 A cm⁻² showed no evidence of degradation. These results strongly suggest that much of the titanium in PEMWEs may be substituted with cheaper, more abundant materials with no loss of electrolyser performance or lifetime, which would significantly reduce the cost of green hydrogen. The combined modelling and experimental approach developed here shows great promise for design optimisation of PEMWEs and other electrochemical energy conversion devices.