In this thesis several aspects of PEM fuel cells are discussed. From an atomic scale, e.g. crystal and electronic structure of a non-noble metal material, e.g. (H)zLiMn2O4 (protonated spinel lithium manganese oxide) for electrocatalysis and its dynamics, to meso-macro scale effects such as those concerning transport resistances at the membrane/electrode interface.

The increasing energy demand of the world population in combination with tangible climate change effects stemming from rising carbon dioxide emissions is currently characterizing a large portion of the political and societal debate. Despite huge technological advancement in the field of renewable energy resulting in energy prices lower than that of fossil based energy, the rate of greenhouse gas emissions has not even levelled off but rather kept increasing. A part of the problem lies in the very nature of season and weather dependent energy conversion technologies producing electricity peaks that are hard to buffer. The solar and wind powered scenario is not yet able to completely replace the relatively demand flexible fossil fuel based power plants. The gap between energy production and energy use, in essence meaning storage and distribution of sustainable energy, constitutes one of the largest challenges of our times. Hydrogen has been proposed as a molecule with the potential of being an important energy carrier in a renewable energy based economy. In a fuel cell, hydrogen can be electrochemically oxidized to water, releasing its chemical energy without the emission of combustion by-products like carbon dioxide. Commonly platinum is used as a catalyst to speed up the anode and cathode reactions in a fuel cell. Reversibly, an electrolyser uses electricity to electrochemically split water into its constituents; hydrogen and oxygen. Ideally, hydrogen could be produced where and when the electricity is available or cheap and be stored or transported to the location where it is needed, although technical challenges as well as infrastructural hurdles are still to be solved. If electrochemical devices, such as fuel cells, are to play a major role in the future energy landscape a better understanding of catalytic processes along with cheap and scalable non-noble metal catalysts are still needed.

In this work, properties of Calcium alginate-reduced graphene oxide and Barium alginate‐reduced graphene oxide composite films are explored. In addition, the properties of the divalent metal ion-cross-linked alginate composite films are compared to the analogous properties of uncross‐linked Sodium alginate-graphene oxide composite films of the corresponding compositions. As the filler, used in the preparation of the composite films, is obtained by chemical oxidation of graphite, the prevailing knowledge of the process coupled with in situ X-ray diffraction investigation of the samples prepared by such a method is presented as well.