Reversible OCP (open circuit potential = open circuit voltage) is the theoretical potential of a reversible electrochemical reaction based on Gibb's free energy / nF; this works out to 1.23 V at STP for the ORR/HOR couple in PEMFCs/AEMFCs and drops to 1.14 V at 100 °C.
Your actual OCV will vary, primarily due to hydrogen crossover, catalyst loading, and how hydrated/swollen your ionomer is - for normally loaded PFSA references at 80 °C I get around 1.00 V and lose around 0.15 V in air.