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A microbial fuel cell (MFC) is an eco-friendly device that uses living microorganisms' catalytic activity for energy harvesting. The power output of this device is still far from the targeted one. An improvement to the power can be accessed via the use of biocompatible high surface area anode materials. Metal-organic frameworks (MOFs) have a high surface area, crystalline, and can be prepared in different morphologies. MOF demonstrated excellent performance in various energy conversion/storage devices. For the first time, a standalone carbon fiber brush electrode modified with Zn-MOF is constructed via a simple hydrothermal approach. The prepared electrodes were investigated as the anode of yeast-based MFC. The MFC with Zn-MOF carbon fiber brush exhibited maximum current and power densities of 317 mA/m2 and 73.7 mW/m2, which are twofold those obtained using bare carbon brush anodes. The significant improvement in the MFC performance with modified carbon fiber brush would be related to the role of the Zn-MOF in facilitating the electron transfer between the anode and the yeast cells and thus promoting bio electrocatalytic activity as confirmed from the redox peaks that appeared during the cyclic voltammetry (CV) of the modified electrodes and supported by electrochemical impedance spectroscopy (EIS). • In-situ Zn-MOF/CB was prepared via hydrothermal method in one-step. • Zn-MOF/CB was investigated for the first time in yeast based MFC. • The modified electrode showed twofold higher power output than the unmodified one. [ABSTRACT FROM AUTHOR]

Nafion membrane is a commercial type of electrolyte membrane that is widely used in low-temperature fuel cells. Nafion membrane is expensive and allows fuel to crossover from anode to cathode. Therefore, it decreases fuel utilization and results in mixed potential at the cathode. Modifying the Nafion membrane and/or replacing it with non-Nafion-based materials has shown promising results in solving these problems. Graphene is a two-dimensional material with exceptional properties that positively affect the performance of several energy conversion/storage devices. With its large surface functional groups, graphene oxide exhibits considerable ionic conductivity with low fuel crossover. This paper reviews and discusses the recent progress in utilizing graphene or its derivatives as a blend with Nafion and non-Nafion based membranes as well as a standalone membrane in low-temperature fuel cells. Graphene or its derivatives possess a high potential as a standalone membrane or a composite membrane in the various low temperature fuel cells applications in terms of high ionic conductivity at low humidity and relevant high temperature, high thermal, mechanical, and chemical stabilities. This work summarizes the recent progress in utilizing graphene and its derivatives (graphene oxide and other doped graphene) in different types of fuel cells, whether as a standalone or as a modifier of the Nafion and non-Nafion based membranes. The review covers the usage of graphene and its derivatives in PEMFCs, DMFCs, anion exchange DMFCs, and MFCs. Furthermore, it elaborates on the science and the engineering aspects of utilizing graphene and its derivatives in different fuel cells. This work demonstrates the importance of the graphene and its derivatives in improving the performance of low temperature fuel cells. • GO promoted high water retention of the fuel cell's membrane. • GO has excellent mechanical, chemical, and thermal stability, and thus its polymer blends gain these properties. • The blends of the electrolyte polymer with GO decreases the fuel crossover. • Applying of graphene as a standalone membrane in PEMFC was summarized. • The performance of Nafion-based and non Nafion-based membranes modified with graphene in fuel cells was summarized. [ABSTRACT FROM AUTHOR]