A critical evaluation of platinum deposition techniques for hydrogen production in microbial electrolysis cells

Despite its high cost, Pt is the usual catalyst for hydrogen production in the cathode of Microbial Electrolysis Cells (MECs). Its effectiveness depends not only on the amount deposited but also on the availability and distribution of Pt nanoparticles on the cathode surface. This work provides a comprehensive study of the effectiveness of the Pt coating with five deposition techniques: spray, electrospray, brush painting, doctor blade and sputtering. The performance of the cathodes was studied with different Pt loadings by monitoring the current intensity and H 2 production in MECs. Furthermore, cathodes were characterized morphologically using scanning electron microscopy together with energy-dispersive X-ray spectroscopy to study their Pt surface distribution and composition. Sputtering was initially discarded due to Pt detachment. When using the same amount of Pt (0.50 mg Pt cm −2 ), the highest current density was obtained for electrospray (2.0 mA cm −2 ), followed by spray (1.9 mA cm −2 ), brush painting (1.6 mA cm −2 ) and doctor blade (1.2 mA cm −2 ). Hence, electrospray improved 20 % the results obtained by the default method of brush painting. Electrospray and spray provided better performance because of the direct deposition of Pt on the carbon fibres creating a compact Pt layer on the electrode surface. Furthermore, it was observed that the cell performance decreased significantly with decreasing amount of Pt per cm 2 , observing the best performance with the highest Pt load tested (0.5 mg Pt cm −2 ) regardless of the deposition technique. • Different Pt deposition methods were studied to produce MEC cathodes. • Brush painting, doctor blade, electrospray, spray, and sputtering were compared. • The spraying techniques showed the best long.-term performance >2 m 3 H 2 m −3 d −1 . • Sputtering led to Pt detachment and to a failure in the long-term operation. • MEC performance relies on Pt amount and accessibility (on dispersion technique).