Aqueous Suspensions of Carbon Nanomaterials with Platinum Nanoparticles for Solution-Processed Hydrogen-Producing Electrocatalysts

Abstract

Proton exchange membrane (PEM) water electrolysis is attracting attention as a promising method for producing clean hydrogen (H2) without emitting carbon dioxide. H2 is produced by the reduction of protons at the cathode in a PEM electrolyzer. Platinum on carbon (Pt/C) is extensively used as a cathodic electrocatalyst; however, the aggregation of Pt in Pt/C necessitates high loading to maintain catalytic activity. Therefore, the development of efficient H2 production electrocatalysts with low Pt loadings is necessary. Herein, we report the preparation of electrocatalysts consisting of solution-processed platinum nanoparticle (PtNP)/carbon nanomaterial (CNM) composites using surfactant-free aqueous-dispersed PtNPs as a dispersant for CNMs. Direct aqueous suspension by PtNPs through noncovalent functionalization occurs universally with single-walled carbon nanotubes (SWCNTs), graphene, and acetylene black, yielding the respective composites. In particular, the PtNP/SWCNT nanocomposite electrocatalyst with a PtNP loading of 6 μgPt cm–2 exhibited a high mass activity of 89,300 A gPt –1 at 2.0 V, which is 270 times higher than that of Pt/C (324 A gPt –1 at 2.0 V) with a Pt loading of 2.8 mgPt cm–2. Furthermore, a PEM electrolyzer containing this electrocatalyst exhibited a Faradaic efficiency of 99% and operated continuously for 150 h at 100 mA cm–2 at an estimated cost of US$5.3/(kg H2). Our findings are promising in terms of not only establishing a methodology for reducing PtNP loading to the microgram order but also demonstrating the practical feasibility of H2-production electrocatalysts for PEM electrolyzers.