Pd@TiO2/Carbon Nanohorns electrocatalysts: Reversible CO2 hydrogenation to formic acid

Michele Melchionna, Victoria Bracamonte, Angela Giuliani, Lucia Nasi, Tiziano Montini, Claudio Tavagnacco, Marcella Bonchio, P Fornasiero, Maurizio Prato

Index: 10.1039/C7EE03361C

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Abstract

Direct conversion of carbon dioxide to formic acid at thermodynamic equilibrium is a privilege of enzymatic catalysis, hardly replicated by synthetic analogs, but of high priority for carbon-neutral energy schemes. The bio-mimetic potential of totally inorganic Pd@TiO2 nanoparticles is envisioned herein in combination with Single Walled Carbon NanoHorns (SWCNHs). The high surface nano-carbon entanglement templates a wide distribution of “hard-soft” bimetallic sites where the small Pd nanoparticles (1.5 nm) are shielded within the TiO2 phase (Pd@TiO2), while being electrically wired to the electrode by the nanocarbon support. This hybrid electrocatalyst activates CO2 reduction to formic acid at near zero overpotential in aqueous phase (onset potential at E < -0.05 V vs RHE, pH = 7.4), while being able to evolve hydrogen via sequential formic acid dehydrogenation. The net result hints at a unique CO2 “circular catalysis” where formic acid versus H2 selectivity is adressable by flow-reactor technology.