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This paper proposes a novel robust model-free adaptive interval type-2 fuzzy sliding mode control (MF-AIT2FSMC) for the proton exchange membrane fuel cell (PEMFC) system using nonlinear disturbance observer. The main control objective is to adjust the oxygen stoichiometry at its reference trajectory under load disturbances and parameter uncertainties, to avert the oxygen starvation problem and to obtain maximum net power. The referred MF-AIT2FSMC control strategy is composed of three parts: first, a nonlinear disturbance observer is proposed to estimate both oxygen and nitrogen partial pressures which are considered as unmeasurable variables. Second, a nonlinear disturbance observer-based intelligent proportional-integral (NDBO-iPI) control is derived, whereas the NDBO is used to estimate the unmodeled system dynamics via the knowledge of input and output signals. Third, adaptive interval type-2 fuzzy nonsingular fast terminal sliding mode control is inserted to NDBO-iPI control to compensate the NDBO estimation error, enhance the control performance and ensure the global controlled system stability. Furthermore, the entire controlled system stability is verified via the Lyapunov approach. Finally, the corresponding numerical simulation on the PEMFC system is obtained to demonstrate the effectiveness and efficiency of the proposed MF-AIT2FSMC technique by comparing with the NDBO-iPI and standard PID controller. [ABSTRACT FROM AUTHOR]