A molecular approach to an electrocatalytic hydrogen evolution reaction on single-layer graphene

Abstract

A major challenge in the development of electrocatalysts is to determine a detailed catalysis mechanism on a molecular level for enhancing catalytic activity. Here, we present bottom-up studies for an electrocatalytic hydrogen evolution reaction (HER) process through molecular activation to systematically control surface catalytic activity corresponding to an interfacial charge transfer in a porphyrin monolayer on inactive graphene. The two-dimensional (2D) assembly of porphyrins that create homogeneous active sites (e.g., electronegative tetrapyrroles (N)) on graphene showed structural stability against electrocatalytic reactions and enhanced charge transfer at the graphene-liquid interface. Performance operations of the graphene field effect transistor (FET) were an effective method to analyse the interfacial charge transfer process associated with information about the chemical nature of the catalytic components. Electronegative pristine porphyrin or Pt-porphyrin networks, where intermolecular hydrogen bonding functioned, showed larger interfacial charge transfers and higher HER performance than Ni-, or Zn-porphyrin. A process to create surface electronegativity by either central N or metal (M)-N played an important role in the electrocatalytic reaction. These findings will contribute to an in-depth understanding at the molecular level for the synergetic effects of molecular structures on the active sites of electrocatalysts toward HER.

Function of Tetra (4-Aminophenyl) Porphyrin in Altering the Electronic Performances of Reduced Graphene Oxide-Based Field Effect Transistor

“…In Figure 2C, it is found that the highest mobilities of holes and electrons are possessed by the reduced GO&TAP ( n = 4). It is in agreement with TAP-enhanced rGO conductance [11] and porphyrin’s catalysis in HER, which is helpful to accelerate the charge transfer in the channel [13]. However, deviations are still observed here, which include: no increasements could be found when the TAP contents are increased from 1/4 ( n = 4) to 1/2 ( n = 2) and from zero (rGO) to 1/8 of GO ( n = 8).…”

“…Later, in the nonlinear optical study of a GO and tetra (4-aminophenyl) porphyrin (TAP) hybrid, an electron and/or energy transfer from photoexcited TAP to its covalently linked GO moiety was also manifested [12]. Motivated by those fundamental studies, more interesting studies about the physicochemical mechanism between porphyrin and graphene [13], as well as the applications of their hybrids, have been reported. For instance, the decorated rGO-based field effect transistor (rGO-FET) by the composite of Fe(III) meso-tetra (4-carboxyphenyl) porphyrin (FeTCP) and rGO (FGPCs) was reported to realize the ultrasensitive NO detection under a lower driving voltage (V DS = 0.1 V) [14], in which the mechanism for the increased sensitivity was ascribed to the charge transfer between porphyrin and rGO, just in accordance with the recent publication about porphyrin-facilitated hydrogen evolution reaction (HER) at the solution–graphene interface [13].…”

“…Motivated by those fundamental studies, more interesting studies about the physicochemical mechanism between porphyrin and graphene [13], as well as the applications of their hybrids, have been reported. For instance, the decorated rGO-based field effect transistor (rGO-FET) by the composite of Fe(III) meso-tetra (4-carboxyphenyl) porphyrin (FeTCP) and rGO (FGPCs) was reported to realize the ultrasensitive NO detection under a lower driving voltage (V DS = 0.1 V) [14], in which the mechanism for the increased sensitivity was ascribed to the charge transfer between porphyrin and rGO, just in accordance with the recent publication about porphyrin-facilitated hydrogen evolution reaction (HER) at the solution–graphene interface [13]. Moreover, based on the similar HER principle, the hybrid of TAP and rGO (TAP-rGO) was also exploited as the channel material in bio-FET and applied for the detection of circulating tumor cells [2].…”

“…According to the summary of those works, it could been perceived that porphyrin can provide modulations in the process of rGO preparation and/or carriers’ transfer in FET: in the raw material preparation stage, it can stabilize GO dispersion [11], or form amide linkages with GO fragments [12]; in the chemical reduction stage, the porphyrin-stabilized GO dispersion may be reduced more deeply [11], and its catalysis in ORR is also helpful for the deoxygenation process [9]; in the working stage of FET, surface-modified porphyrin can facilitate charge transfer at the solid–liquid interface [13], and the similar HER effect is also found in porphyrin–rGO hybrid decorated [14] and channeled [2] FETs. Although it was believed that the hybrid of TAP and rGO can have a positive influence on FET’s electronic performances, the study of TAP’s function from the point of view of FET has not been found.…”

Earth‐Abundant Transition‐Metal‐Based Bifunctional Electrocatalysts for Overall Water Splitting in Alkaline Media

“…reported an effective method to prepare P‐doped crystalline arrays of NiMo 4 N 5 by using polymolybdic acid and nickel nitrate as metal sources to provide a high surface‐to‐volume ratio of energetic actives, which approached a current density of 50 and 100 mA cm −2 for water splitting at low cell voltages of 1.59 and 1.66 V, respectively . Moreover, the incorporation of multiple non‐metal (B, N, and S) heteroatoms by synergistic coupling with their single‐doped counterparts has been proposed as an alternative method to produce rapid interfacial charge transfer within the hybrid composites…”