Platinum-decorated carbon nanotubes for hydrogen oxidation and proton reduction in solid acid electrochemical cells

Pt-decorated carbon nanotubes (Pt-CNTs) were used to enhance proton reduction and hydrogen evolution in solid acid electrochemical cells based on the proton-conducting electrolyte CsH₂PO₄. The carbon nanotubes served as interconnects to the current collector and as a platform for interaction between the Pt and CsH₂PO₄, ensuring minimal catalyst isolation and a large number density of active sites. Particle size matching was achieved by using electrospray deposition to form sub-micron to nanometric CsH₂PO₄. A porous composite electrode was fabricated from electrospray deposition of a solution of Pt-CNTs and CsH₂PO₄. Using AC impedance spectroscopy and cyclic voltammetry, the total electrode overpotential corresponding to proton reduction and hydrogen oxidation of the most active electrodes containing just 0.014 mg cm^-1 of Pt was found to be 0.1 V (or 0.05 V per electrode) at a current density of 42 mA cm^-2 for a measurement temperature of 240°C and a hydrogen-steam atmosphere. The zero bias electrode impedance was 1.2 Ω cm², corresponding to a Pt utilization of 61 S mg^-1, a 3-fold improvement over state-of-the-art electrodes with a 50× decrease in Pt loading.