The combined influence of factors, that is, operating cell temperature, humidification temperature (HT) (indirectly relative humidity), and reactant gas inletline temperature on the performance of proton exchange membrane fuel cell was experimentally and statistically studied. A catalyst-coated membrane, membrane electrode assembly, of 6.25 cm 2 active area and 0.29 mg pt cm -2 catalyst loading was used in the study. Experimentally, the effect of individual factors and their combinations on cell performance was studied. Statistical analyses were carried out to find the main and interaction effects of different factors. Analysis of variance (ANOVA, 5% significance level, 95% confidence level) analysis, which was validated for homoscedasticity, was used to evaluate the significance of the main and interaction effects of factors. From the study, it was observed that the HT had a significant main effect (988 W m -2 ). Both interaction plots and ANOVA results revealed that the combination of operating cell and HT was the most significant. The study showed a very interesting observation that the statistical interaction effect (545 W m -2 ) was half of the experimental deviation value (1090 W m -2 ) between the summation of independent effects and the combined effect. K E Y W O R D Sexperimental deviation value, humidification temperature, inlet-line temperature, operating cell temperature, proton exchange membrane fuel cell List of Symbols: 𝐸𝑓𝑓𝑒𝑐𝑡 𝑚𝑎𝑖𝑛 , main effect (in terms of peak power density) (W m -2 ); 𝐸𝑓𝑓𝑒𝑐𝑡 𝑖𝑛𝑡𝑒𝑟𝑎𝑐𝑡𝑖𝑜𝑛 , interaction effect (in terms of peak power density) (W m -2 ); {[𝑃 𝑝𝑒𝑎𝑘 𝑎𝑣𝑔 ] ℎ𝑖𝑔ℎ } 𝑖𝑛𝑡𝑒𝑟𝑎𝑐𝑡𝑖𝑜𝑛 , average of peak power densities when the interaction was at a high level (W m -2 ); {[𝑃 𝑝𝑒𝑎𝑘 𝑎𝑣𝑔 ] 𝑙𝑜𝑤 } 𝑖𝑛𝑡𝑒𝑟𝑎𝑐𝑡𝑖𝑜𝑛 , average of peak power densities when the interaction was at a low level (W m -2 ); {[𝑃 𝑝𝑒𝑎𝑘 𝑎𝑣𝑔 ] 𝑙𝑜𝑤 } 𝐴 & 𝐵 , average of peak power densities when factors A and B were at a low level (W m -2 ) (can be applied for other factors too); {[𝑃 𝑝𝑒𝑎𝑘 𝑎𝑣𝑔 ] ℎ𝑖𝑔ℎ } 𝐴 & 𝐵 , average of peak power densities when factors A and B were at a high level (W m -2 ) (can be applied for other factors too); {[𝑃 𝑝𝑒𝑎𝑘 𝑎𝑣𝑔 ] 𝑙𝑜𝑤 & ℎ𝑖𝑔ℎ } 𝐴 & 𝐵 , average of peak power densities when factors A and B were at low and high levels, respectively (W m -2 ) (can be applied for other factors too); {[𝑃 𝑝𝑒𝑎𝑘 𝑎𝑣𝑔 ] ℎ𝑖𝑔ℎ & 𝑙𝑜𝑤 } 𝐴 & 𝐵 , average of peak power densities when factors A and B were at high and low levels, respectively (W m -2 ) (can be applied for other factors too); Δ[𝑃 𝑝𝑒𝑎𝑘 𝑎𝑣𝑔 ] 𝑐𝑜𝑚𝑏𝑖𝑛𝑒𝑑 𝑒𝑓𝑓𝑒𝑐𝑡 , reduction in average peak power density value due to combined effect (W m -2 ); ∑ {Δ[𝑃 𝑝𝑒𝑎𝑘 𝑎𝑣𝑔 ] 𝑖𝑛𝑑𝑒𝑝𝑒𝑛𝑑𝑒𝑛𝑡 𝑒𝑓𝑓𝑒𝑐𝑡𝑠 }, summation of deviation in average power density in independent effects (W m -2 )

The present study mainly focuses on the different combinations of significant operating parameters like inlet relative humidity of anode gas and cathode gas, operating pressure and nature of cathode gas on the performance of Proton Exchange Membrane Fuel Cell (PEMFC) using validated three- dimensional (3D), single-phase, and non-isothermal model with the help of ANSYS Fluent 18.1 package. The results of different combinations on the performance of PEMFC are compared with independent effects of the operating parameters. Results revealed that the combined operating parameters? effect on the performance of the PEMFC is deviated significantly (up to 5 %) compared to the expected summation of individual parameters effect which is considerable in fuel cell scaling and stack applications. Nature of gas, operating pressure, and inlet cathode gas relative humidity are the most significant parameters in the automobile applications which have to be dealt with care where the combination of changes in operating parameters is quite phenomenal.