Platinum Graphene Catalytic Condenser for Millisecond Programmable Metal Surfaces

Abstract

Accelerating catalytic chemistry and tuning surface reactions require precise control of the electron density of metal atoms. In this work, nanoclusters of platinum were supported on a graphene sheet within a catalytic condenser device that facilitated electron or hole accumulation in the platinum active sites with negative or positive applied potential, respectively. The catalytic condenser was fabricated by depositing on top of a p-type Si wafer an amorphous HfO 2 dielectric (70 nm), on which was placed the active layer of 2−4 nm platinum nanoclusters on graphene. A potential of ±6 V applied to the Pt/graphene layer relative to the silicon electrode moved electrons into or out of the active sites of Pt, attaining charge densities more than 1% of an electron or hole per surface Pt atom. At a level of charge condensation of ±10% of an electron per surface atom, the binding energy of carbon monoxide to a Pt(111) surface was computed via density functional theory to change 24 kJ mol −1 (0.25 eV), which was consistent with the range of carbon monoxide binding energies determined from temperature-programmed desorption (ΔBE CO of 20 ± 1 kJ mol −1 or 0.19 eV) and equilibrium surface coverage measurements (ΔBE CO of 14 ± 1 kJ mol −1 or 0.14 eV). Impedance spectroscopy indicated that Pt/graphene condensers with potentials oscillating at 3000 Hz exhibited negligible loss in capacitance and charge accumulation, enabling programmable surface conditions at amplitudes and frequencies necessary to achieve catalytic resonance.

Energy Flows in Static and Programmable Catalysts

“…26 Alternatively, when ∼4 nm Pt nanoparticles on graphene formed the active layer atop a catalytic condenser, variable application of −6 V to +6 V altered the binding of carbon monoxide by ∼20 kJ/mol. 29 The catalytic condenser can be oscillated as fast as ∼3,000 Hz, switching between ±6 V without any loss in maximum accumulated charge in the catalyst layer. 29 By this platform approach, energy flowing to the active layer through current can be tuned in voltage to rapidly change the binding behavior of molecules over a broad range of materials and large changes in the heat of adsorption.…”

“…29 The catalytic condenser can be oscillated as fast as ∼3,000 Hz, switching between ±6 V without any loss in maximum accumulated charge in the catalyst layer. 29 By this platform approach, energy flowing to the active layer through current can be tuned in voltage to rapidly change the binding behavior of molecules over a broad range of materials and large changes in the heat of adsorption.…”

“…With an active layer of ∼4 nm of amorphous alumina on graphene, condensation of holes at the surface increased the binding energy of isopropanol by ∼20 kJ/mol . Alternatively, when ∼4 nm Pt nanoparticles on graphene formed the active layer atop a catalytic condenser, variable application of −6 V to +6 V altered the binding of carbon monoxide by ∼20 kJ/mol . The catalytic condenser can be oscillated as fast as ∼3,000 Hz, switching between ±6 V without any loss in maximum accumulated charge in the catalyst layer .…”

“…Unlike the ATP-to-ADP reaction which provides 0.29–0.36 eV per reacting ATP molecule, programmable catalytic systems can input a continuum range determined by the energy delivery mechanism. For example, larger changes in voltage applied to a catalytic condenser yields larger changes in surface binding energy . A significant advantage of inorganic programmable devices is the ability to precisely apply energy inputs or outputs with broader range and more temporal specificity.…”

“…For example, larger changes in voltage applied to a catalytic condenser yields larger changes in surface binding energy. 29 A significant advantage of inorganic programmable devices is the ability to precisely apply energy inputs or outputs with broader range and more temporal specificity. The destination of energy put into a programmable catalyst is determined by both the mechanism of energy transfer and the energetics of the entire programmable catalyst cycle (states 2→1→2).…”