Graphene Formation Mechanism by the Electrochemical Promotion of a Ni Catalyst

Abstract

In this work, we show that multilayer graphene forms by methanol decomposition at 280 °C on an electrochemically promoted nickel catalyst film supported on a K-βAl2O3 solid electrolyte. In operando near ambient pressure photoemission spectroscopy and electrochemical measurements have shown that polarizing negatively the Ni electrode induces the electrochemical reduction and migration of potassium to the nickel surface. This elemental potassium promotes the catalytic decomposition of methanol into graphene and also stabilizes the graphene formed via diffusion and direct K–C interaction. Experiments reveal that adsorbed methoxy radicals are intermediate species in this process and that, once formed, multilayer graphene remains stable after electrochemical oxidation and back migration of potassium to the solid electrolyte upon positive polarization. The reversible diffusion of ca. 100 equivalent monolayers of potassium through the carbon layers and the unprecedented low-temperature formation of graphene and other carbon forms are mechanistic pathways of high potential impact for applications where mild synthesis and operation conditions are required.

A Discussion on the Unique Features of Electrochemical Promotion of Catalysis (EPOC): Are We in the Right Path Towards Commercial Implementation?

“…This explains why, upon the application of positive polarizations, H 2 is desorbed and released under inert atmosphere, as it can be observed in Figure 6b. It should be noted that the in-situ controlled K + supply and the formation of graphene-like species on the surface of this nanoporous Ni/K + -βAl 2 O 3 electrochemical catalyst has been proved by Espinós et al in two recent studies by in operando near-ambient pressure photoemission (NAPP) spectroscopy [111,112]. The main weakness of this EPOC approach on hydrogen production/storage is its complexity since it involves not only the catalyst film and the solid electrolyte but also the carbonaceous species generated during the methanol reforming reaction.…”

Surface coverage control for dramatic enhancement of thermal CO oxidation by precise potential tuning of metal supported catalysts

“…20 The modied surface exhibits adsorption properties distinct from its opencircuit counterpart, i.e., without the applied voltage; the surface catalyzes the reaction with lessened activation energy. [20][21][22] The utilization of such in situ WF alteration enhanced the catalytic performance of thermodynamically-allowed reactions with multi-fold rates and/or selectivity compared to that at opencircuit; representative reactions include (oxygenated) hydrocarbon oxidation, 23,24 CO 2 hydrogenation, 25,26 graphene synthesis, 22 and alcohol dehydration. 27 The employment of electrochemical promotion was later extended to a few systems consisting of a liquid electrolyte at room temperature.…”

“…, without the applied voltage; the surface catalyzes the reaction with lessened activation energy. 20–22 The utilization of such in situ WF alteration enhanced the catalytic performance of thermodynamically-allowed reactions with multi-fold rates and/or selectivity compared to that at open-circuit; representative reactions include (oxygenated) hydrocarbon oxidation, 23,24 CO 2 hydrogenation, 25,26 graphene synthesis, 22 and alcohol dehydration. 27…”