A Comparative Electrochemical Study of Pt and Ni–Oxide Cathodes: Performance and Economic Viability for Scale-Up Microbial Fuel Cells

The expensive nature and limited availability of platinum (Pt) cathodes pose a significant challenge for the widespread adoption of microbial fuel cell (MFC) technology. Although many alternatives have been studied, very few reports provide a systematic head-to-head comparison of different Ni–oxide cathodes under the same operational conditions. This research investigates cost-effective nickel-based metal oxide composites (Ni–TiO2, Ni–Cr2O3, Ni–Al2O3) as catalysts for the oxygen reduction reaction (ORR), using Pt as a reference point. The performance of the MFC was thoroughly evaluated in terms of power output, chemical oxygen demand (COD) removal, and Coulombic efficiency (CE). The Pt cathode exhibited the highest performance (275 mW m−2, 87% COD removal, 35% CE), confirming its catalytic advantages. Among the alternative materials, the Ni–TiO2 composite yielded the best outcomes (224 mW m−2, 79% COD removal, 17.7% CE), markedly surpassing the performances of Ni–Cr2O3 (162 mW m−2, 72%, 24% CE) and Ni–Al2O3 (134 mW m−2, 64%, 11.6% CE). Koutecký–Levich analysis clarified the mechanisms at play: Pt facilitated a direct 4-electron ORR process, while the composites operated through a 2-electron mechanism. Notably, the semiconductor properties of Ni–TiO2 resulted in a higher electron transfer number (n = 2.8) compared to the other composites (n ≈ 2.3), which accounts for its increased efficiency. With its low production cost, Ni–TiO2 presents an exceptional cost-to-performance ratio. By linking catalytic performance directly to the electronic nature of the oxide supports, this study offers clear design guidelines for selecting non-precious cathodes. The dual evaluation of electrochemical efficiency and cost-to-performance distinguishes this study from prior reports and underscores its practical significance and originality. This study highlights Ni–TiO2 as a highly sustainable and economically viable catalyst, making it a strong candidate to replace Pt for practical MFC applications that focus on simultaneous power generation and wastewater treatment.