Calcium hydroxyapatite nanoparticle-induced bio-electrocatalytic hydrogen production in a single-chambered carbon cloth-based cathodic microbial electrolysis cell

An efficient catalyst is crucial for enhancing hydrogen (H₂) production in microbial electrolysis cell (MEC). In this study, a hydroxyapatite (HA) nanoparticle was developed by coprecipitation and used as a novel catalyst to promote H₂-producing bioelectrochemical reactions from wheat straw wastes in a single chambered carbon cloth-based cathodic microbial electrolysis cell. Results demonstrated that adding 200 mg/L HA in MEC achieved a maximum H₂ yield of 2.4 mmol/g-straw which is ∼1.9 times that of the MEC operated without hydroxyapatite nanoparticles. Moreover, the supply of 200 mg/L HA, promoted substrate utilization and extracellular polymer substance (EPS) formation, and the electrochemical characteristics analyses revealed a decrease both in charge transfer resistance and electrochemical noise measurements, indicating more efficient electron transfer processes. Furthermore, microbial community results showed that hydroxyapatite promoted the proliferation of the well-known potential H₂-producers and electrogenic microbes in MEC-200HA anodic biofilm, including bacillus sp. (23.35 %), clostridium sp. (20.15 %), and members of Ruminococcaseae (11.29 %). These microbes syntrophically bio-oxidized straw biomass and facilitated charge transfer from substrates to electrodes, enhancing H₂ production. This research will pave ways for further optimization of nanoparticle-based catalysts in microbial electrochemical systems, contributing to the advancement of renewable energy technologies.