Bioelectrochemical deposition of palladium nanoparticles as catalysts by Shewanella oneidensis MR-1 towards enhanced hydrogen production in microbial electrolysis cells

Catalysts are critically important to accomplish hydrogen evolution reaction in microbial electrolysis cells (MECs). Herein, palladium nanoparticles were generated directly on a cathode electrode by bioelectrochemical reduction with Shewanella oneidensis MR-1 and then applied to produce hydrogen gas in MECs. The MEC with bioelectrochemically deposited Pd catalysts achieved a hydrogen production rate of 61.8 +/- 2.0 L-H-2 m(-3) d(-1), significantly higher than 38.5 +/- 2.0 L-H-2 m(-3) d(-1) with the Pd catalysts in the absence of microbial reduction. This improvement was related to a higher electrochemical active surface area of 40.5 +/- 3.5 m(2) g(-1) and smaller Pd particle size (10-100 nm) on the cathode with bioelectrochemical deposition, compared to those of electrochemically-generated Pd catalysts (16.8 +/- 2.8 m(2) g(-1) and 200-250 nm, respectively). The superior performance of the bioelectrochemically deposited Pd catalysts was supported by a much smaller charge transfer resistance of 15.4 Omega. Although microorganisms could help generate better Pd catalysts, the lack of strong bond between Pd nanoparticles and carbon cloth resulted in unstable hydrogen production performance. Applying a binding agent - Nafion led to consistent current generation and hydrogen production. The results of this study encourage further exploration of in situ deposition of catalysts via bioelectrochemical reactions for MEC applications. (C) 2019 Elsevier Ltd. All rights reserved.