DEVELOPMENT OF MATERIALS AND ELECTRODES FOR MICROBIAL BIOELECTROLYSIS SYSTEMS AND MONITORING OF MICROBIOLOGICALLY INFLUENCED CORROSION

The global energy transition toward carbon neutrality demands innovative technologies that integrate renewable electricity with sustainable carbon management strategies. This doctoral thesis addresses critical challenges in Power-to-X systems by investigating three interconnected research areas: oxygen evolution reaction (OER) electrocatalysis for efficient hydrogen production, microbiologically influenced corrosion (MIC) in biological methanation environments, and bioelectrochemical CO₂ conversion using alternative inocula from geothermal emissions. The first part focuses on reducing precious metal demand in proton exchange membrane water electrolysis by rational catalyst design. A core-shell IrO2@TiO2 catalyst was developed by depositing ultrathin IrO2 layers onto rutile TiO2 supports, achieving electrochemical performance comparable to commercial IrO2 while drastically lowering iridium loading. Crystallographic compatibility between rutile phases enabled superior electronic percolation and iridium utilization, demonstrating that support-catalyst engineering is an effective strategy for precious metal reduction. The second part investigates the complex interplay between metallic (i.e., copper and iron alloys) cathode materials, microbial inocula, and corrosion phenomena in bioelectrochemical systems. Systematic comparison of biotic, thermally treated, and sterile conditions applied to a biomethanation inoculum revealed that complete sterilization consistently led to the most severe corrosion in all tested metal coupons, while controlled thermal treatments of the inoculum enabled selective enrichment of microorganisms capable of protective biomineralization. Across all materials, corrosion mitigation was governed primarily by solution chemistry, particularly carbonate and phosphate availability, rather than by microbial activity itself, highlighting the transition from microbiologically influenced corrosion to microbially mediated corrosion inhibition. The third part demonstrates proof-of-concept bioelectrochemical CO2 conversion using alternative inocula from geothermal emissions at the Monte Amiata volcanic complex. Reactor performance was strongly controlled by sulfate concentration in the inoculum, with high sulfate suppressing methanogenesis through competitive sulfate reduction. Stable methane production was achieved only under low-sulfate conditions, forming an acetogenic-methanogenic consortium sustained by continuous electrochemical polarization. This integrated investigation provides fundamental insights into the critical challenges facing Power-to-X deployment. For anodic water oxidation, crystallographic engineering of support-catalyst interfaces enables dramatic precious metal reduction while maintaining performance. For cathodic biomethanation systems, understanding MIC mechanisms reveals that solution chemistry, particularly carbonate and phosphate availability, controls passivation more than microbial presence, with thermal treatment severity determining whether protective or detrimental surface films form. Finally, bioelectrochemical CO2 conversion using geothermal emissions is fundamentally viable but requires rigorous inoculum selection to minimize sulfate-driven metabolic competition, with sustained polarization serving dual functions of driving productive electrosynthesis while preventing electrode passivation. These findings establish a foundation for developing integrated carbon capture and utilization systems that couple renewable electricity with biological CO2 reduction at geothermal sites, while identifying critical materials and operational challenges that must be addressed for practical deployment.