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Grain boundaries critically limit the electronic performance of oxide perovskites. These interfaces lower the carrier mobilities of polycrystalline materials by several orders of magnitude compared to single crystals. Despite extensive effort, improving the mobility of polycrystalline materials (to meet the performance of single crystals) is still a severe challenge. In this work, the grain boundary effect is eliminated in the perovskite strontium titanate by incorporating graphene into the polycrystalline microstructure. An effective mass model provides strong evidence that polycrystalline graphene/strontium titanate nanocomposites approach single crystal-like charge transport. This phenomenological model reduces the complexity of analyzing charge transport properties so that a quantitative comparison can be made between the nanocomposites and strontium titanate single crystals. In other related works, graphene composites also optimize the thermal transport properties of thermoelectric materials. Therefore, decorating grain boundaries with graphene appears to be a robust strategy to achieve "phonon glass–electron crystal" behavior in oxide perovskites. ; This work has received the funding from the European Union's Horizon 2020 research and innovation programme under the Marie Skłodowska-Curie individual Fellowship programme No 800031. The authors gratefully acknowledge the support provided by the EPSRC (awards: EP/I036230/1, EP/L014068/1, EP/L017695/1). The authors would also like to acknowledge funding from the National Science Foundation (DMREF-1729487 and DMREF-1333335). As the Research Chair in Carbon Materials, IAK gratefully acknowledges support from Morgan Advanced Materials/ Royal Academy of Engineering. All research data supporting this publication are directly available within the publication.

This is the final version. Available on open access from Wiley via the DOI in this record ; Simple, yet versatile, methods to functionalize graphene flakes with metal (oxide) nanoparticles are in demand, particularly for the development of advanced catalysts. Herein, we report a laserassisted, continuous, solution route for the simultaneous reduction and modification of graphene oxide with catalytic nanoparticles. Electrochemical graphene oxide (EGO) was used as both the starting material and electron-hole pair source due to its low degree of oxidation, which imparts structural integrity and an ability to withstand photo-degradation. Simply illuminating a stream containing EGO and metal salt precursor solutions(e.g. H2PtCl6 or RuCl3) with a 248 nm wavelength laser produced reduced EGO (rEGO, oxygen content 4.0 at.%) flakes decorated with Pt (~2.0 nm) or RuO2 (~2.8 nm) nanoparticles. The RuO2-rEGO flakes exhibited superior catalytic activity for the oxygen evolution reaction, requiring a small overpotential of 225 mV to reach a current density of 10 mA cm−2 . Whereas, the Pt-rEGO flakes shows significantly enhanced mass activity for the hydrogen evolution reaction and a similar performance for oxygen reduction reaction compared to a commercial 20% Pt/C catalyst. This simple production method was also used to deposit PtPd alloy and MnOx nanoparticles on rEGO , demonstrating its versatility in synthesizing functional nanoparticle-modified graphene materials. ; University of Manchester ; Engineering and Physical Sciences Research Council (EPSRC) ; European Union Horizon 2020