Modulating Electrocatalysis on Graphene Heterostructures: Physically Impermeable Yet Electronically Transparent Electrodes

Abstract

The electronic properties and extreme thinness of graphene make it an attractive platform for exploring electrochemical interactions across dissimilar environments. Here, we report on the systematic tuning of the electrocatalytic activity toward the oxygen reduction reaction (ORR) via heterostructures formed by graphene modified with a metal underlayer and an adlayer consisting of a molecular catalyst. Systematic voltammetric testing and electrochemical imaging of patterned electrodes allowed us to confidently probe modifications on the ORR mechanisms and overpotential. We found that the surface configuration largely determined the ORR mechanism, with adlayers of porphyrin molecular catalysts displaying a higher activity for the 2e pathway than the bare basal plane of graphene. Surprisingly, however, the underlayer material contributed substantially to lower the activation potential for the ORR in the order Pt > Au > SiO , strongly suggesting the involvement of the solution-excluded metal on the reaction. Computational investigations suggest that ORR enhancements originate from permeation of metal d-subshell electrons through the graphene layer. In addition, these physically impermeable but electronically transparent electrodes displayed tolerance to cyanide poisoning and stability toward long-term cycling, highlighting graphene as an effective protection layer of noble metal while enabling electrochemical interactions. This work has implications in the mechanistic understanding of 2D materials and core-shell-type heterostructures for electrocatalytic reactions.

Rotational dynamics of the organic bridging linkers in metal–organic frameworks and their substituent effects on the rotational energy barrier

“…[31][32][33][34][35][36][45][46][47][48] As stated earlier, Grimme and co-workers [37][38][39] introduced an improved version of the semi-empirical hybrid DFT method, DFT-D3, 38,40 which incorporates an additional term in the represented by the white, grey, dark yellow, red, and blackish red colours respectively, and S1, S2, and S3 are the imaginary planes. [37][38][39] demonstrated that using the DFT-D method with the z quality basis sets much of the basis set superposition error (BSSE) calculation is avoided, [37][38][39][48][49][50] which is otherwise essential for highly correlated methods like MP2 and coupled-cluster single double (triple) (CCSD(T)) methods. In fact, the BSSE is absorbed into the empirical potential showed by Grimme and co-workers.…”

“…A very accurate geometry and thermochemistry can be obtained by this DFT-D functional when the systems are covalently bonded and weakly bound vdW dominated by long-range dispersion forces. 35,36,[48][49][50] During the optimization, we have considered planar rigidity constraint condition with three imaginary planes, S1 (y-z plane), S2 (y-z plane) and S3 (x-z plane), as shown in Fig. 2 and 3, to incorporate imaginary crystal effects as well as to keep the planar rigid MOFs structure without any distortion.…”

Adiabatic versus Non-Adiabatic Electron Transfer at 2D Electrode Materials

“…Depending on the electrode reaction, consideration needs to the effect of atmospheric contamination or exposure to ambient conditions, of the graphene sample. 16,36,38,66,84,95 An important point to bear in mind for SECCM studies of graphene, 36,38 and also for other local electrochemical measurements, 23,29 is that because all of the different structural motifs are assessed on the same sample, they all have the same history. The [Ru(NH3)6] 3+/2+ process displays fast kinetics on carbon electrode materials even after extensive exposure to ambient atmosphere, 66,95,96 and so we can be confident in the ratio of ET kinetics measured at monolayer and bilayer graphene for comparison to theory.…”

“…33,34 Many previous electrochemistry studies of graphene (both exfoliated and grown by chemical vapor deposition) have considered material transferred to a Si/SiO2 surface. 23,29,[35][36][37][38][39][40][41][42][43] The study of graphene as-grown on copper not only allows back contact for electrochemistry, 27 but negates the need for polymeric transfer to a substrate, which may significantly contaminate the graphene surface and the resulting electrochemistry. 44 Furthermore, as-grown graphene on copper presents small islands of bilayer and multilayer graphene 45,46 on a contiguous monolayer of graphene/copper.…”

Adiabatic versus Non-Adiabatic Electron Transfer at 2D Electrode Materials

“…20 We examine adiabatic vs. non-adiabatic OS-ET using 2D electrode materials on a conducting support. This electrode configuration is of growing interest [21][22][23][24][25][26][27] because electrochemical activity can be modulated and controlled via the electronic interaction of the metal back contact/2D material. 23,25,26,[28][29][30][31][32] The studies herein consider graphene grown on copper (Cu) foil by chemical vapor deposition (CVD) to address the question of adiabatic vs. non-adiabatic OS-ET, and to provide a new perspective on electronic control of electrochemistry at metal-supported graphene.…”