NOVELTY - A non-woven fiber web comprises several fibers (A) which are oriented in x-, y- and optionally z- directions. The fibers (A) are bonded with a polymeric substance. One or more continuous strands are embedded within sub-surface layer of non-woven web. Each continuous strand comprises several carbon fibers (B).    USE - Useful as base structure for gas diffusion substrate, gas diffusion electrode and membrane electrode assembly which are used for fuel cell. The non-woven fibrous web are used for metal-air batteries, electrochemical gas sensors, electrochemical reactors for the electrosynthesis of useful chemical compounds and separator mats for batteries. The non-woven fibrous web is used in composite materials for cryogenic insulation, composite reinforcements such as plastics, cements, printed circuit boards, sports goods for insulation purposes, military applications, automotive structural components, brakes, gaskets, transmission units and for filtration applications.    ADVANTAGE - The compressibility of the substrate or the electrode is reduced significantly when the non-woven fibrous web is used as base structure and consequently the amount of movement experienced during compression of stack, is reduced. The tendency of the substrate or electrode to distort into channels and restriction of gas flow are reduced significantly. The fuel stacks are operated at ambient pressure.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are also included for the following: (i) gas diffusion substrate which comprises a non-woven fibrous web under filler material. The filler material comprises base filler material and optionally one or more modifying metals; (ii) gas diffusion electrode which comprises gas diffusion substrate and electrocatalyst material; (iii) membrane electrode assembly which comprises gas diffusion electrode, another gas diffusion electrode and solid polymer membrane; and (iv) fuel cell comprising gas diffusion substrate, gas diffusion electrode or membrane electrode assembly.