Nitrogen-Mediated Graphene Oxide Enables Highly Efficient Proton Transfer

Abstract

Two-dimensional (2D) graphene and graphene oxide (GO) offer great potential as a new type of cost-efficient proton-exchange membranes (PEM) for electrochemical devices. However, fundamental issues of proton transfer mechanism via 2D membranes are unclear and the transfer barrier for perfect graphene are too high for practical application. Using ab initio molecular dynamic simulations, we screened the proton transfer barrier for different un-doped and nitrogen doped GO membranes, and clarified the corresponding transfer mechanisms. More significantly, we further identify that N-mediated GO can be built into a highly efficient PEM with a proton transfer rate of seven orders of magnitude higher than an un-doped case via. a proton relay mechanism between a ketone-like oxygen and a pyridine-like nitrogen across the vacancy site. The N-doped 2D GO is also impermeable to small molecules, and hence a highly efficient PEM for practical applications.

Biomimetic N-Doped Graphene Membrane for Proton Exchange Membranes

“…The doped nitrogen atoms in graphene, both pyrrolic and graphitic ones, induced localized electrons, , which can form a transient coordination bond with the proton to assist the transmembrane proton transport (for a detailed discussion, see Supporting Information section 2). This mechanism is supported by the previous work on a similar system, which studied the proton transport across N-doped graphene oxide based on the first principle calculations . The assisting role of N-doping in proton transport was reflected by the increase in the measured areal conductivity of 1 M HCl across the fabricated membranes (Figure b).…”

“…This mechanism is supported by the previous work on a similar system, which studied the proton transport across N-doped graphene oxide based on the first principle calculations. 41 The assisting role of N-doping in proton transport was reflected by the increase in the measured areal conductivity of 1 M HCl across the fabricated membranes (Figure 1b). Compared with the reported proton permeance of perfect exfoliated monolayer graphene without defects, the proton permeance of the pristine CVD growth graphene in our experiment was ∼30 times higher.…”

“…After N-doping within 1 min of plasma treatment, the coordination interaction lowers the energy barrier for transmembrane proton transport 41 and increases the selectivity of protons over counterions to ∼40 (Figure 2c), which was more than 2 times higher than the commercial Nafion PEMs (Figure 2d). The selectivity then decreased with longer treatment duration due to the generation of large nanopores in the membrane through which both H + and Cl − can permeate.…”