Designed Catalytic Protocol for Enhancing Hydrogen Evolution Reaction Performance of P, N-Co-Doped Graphene: The Correlation of Manipulating the Dopant Allocations and Heteroatomic Structure

Abstract

Even though “metal-free” carbonaceous electrocatalysts like heteroatom(s)-doped graphene exhibit several advantages, such as cost-effectiveness and high stability toward hydrogen evolution reaction (HER), and are expected to approach the HER performance of Pt, due to the lack of appropriate techniques for completely tailoring the allocation (proportion, content, and configuration) of the dopants and their dominant functionalities, their actual HER performance till date is worse than that of their metallic counterparts. Although it is extremely desirable, the effort to address this issue is scarce in the literature. In the present study, for the first time, we report a facile and simple methodology of the stepwise optimization of dopant allocation, taking P, N-co-doped graphene as a model system. In a two-step synthetic procedure, through the systematic variation of the precursor amount in the first step (optimization of composition) solely, we attempted to obtain a minimum N/P ratio (=2.04) at maximum N (=9.8%) and P (=4.8%) doping levels, while maintaining the optimized bonding configurations by controlling the NH3 pyrolysis parameters in the second step. The composition-optimized structure resulted in a unique configuration having an optimum pyN (pyridinic-N)/gN (graphitc-N) ratio (=5.75%) and relatively high PC (P–C bond)/PO (P–O bond) ratio (=3.29) at a nearly unaltered N/P ratio (=2.33). Further, we have found a protocol which demonstrates that for the coarse alteration of overpotential [@10 mA cm–2 (η10)], the N/P ratio should be tailored, while for a fine alteration, the pyN/gN ratio should be tailored, thus providing a “rule-of-thumb” for obtaining the best “metal-free” co-doped carbonaceous HER catalysts with the best dopant allocations. This, in our case, resulted in enhanced HER performance exhibiting a η10 of 338 mV and Tafel slope of 88 mV dec–1. This extremely low Tafel slope is comparable to or better than many of the “metal-free” heteroatom(s)-doped carbonaceous and state-of-the-art metallic HER catalysts. The stepwise dopant allocations, which also involves switching the dopant type and the established protocol, may be a step forward towards the design of highly efficient metal-free catalysts for the excellent water splitting performance.

Heteroatom-Doped Flash Graphene

“…The elemental ratio of N is ∼5.4% (Figure S7), the majority of which is in the form of pyridinic N (∼398.7 eV) and pyrrolic N (∼399.8 eV), with no indication of N-oxides (Figure d, Table S2). The ratio of pyridinic N and graphitic N reaches ∼4.31 . These pyridinic N atoms have unpaired electron spin density and exhibit strong interactions with some species, like metal atoms, which is useful in potential applications in electrocatalysts or metal electrodeposition. , An appreciable valence band maximum (VBM) of −2.51 eV is measured for N-FG (Figure e).…”

“…The ratio of pyridinic N and graphitic N reaches ∼4.31. 37 These pyridinic N atoms have unpaired electron spin density and exhibit strong interactions with some species, like metal atoms, which is useful in potential applications in electrocatalysts or metal electrodeposition. 10,25 An appreciable valence band maximum (VBM) of −2.51 eV is measured for N-FG (Figure 2e).…”

Metal–Organic Framework–Based CoS2 Nitrogen‐Doped Carbon for High‐Performance Lithium Storage

“…Despite great advancements, design and construction of carbon‐based anode material with outstanding lithium storage performance is still an urgent but inevitable challenge for meeting the demands of lithium‐based rechargeable batteries. [ 23–27 ]…”

“…Despite great advancements, design and construction of carbon-based anode material with outstanding lithium storage performance is still an urgent but inevitable challenge for meeting the demands of lithium-based rechargeable batteries. [23][24][25][26][27] Herein, we designed and synthesized a series of CoS 2embedded triple N-doped carbon dodecahedral frameworks composites utilizing a simple two-step heat-treatment approach and a cobalt-based zeolite imidazole framework (ZIF-67) as the precursor. Then, we made the composite materials as the negative electrode of the battery.…”

Sulfide with Oxygen-Rich Carbon Network for Good Lithium-Storage Kinetics

“…Moreover, the electrocatalytic activity of the electrode materials for alkali metal-ion batteries has also attracted much attention recently in view of reducing the overpotential, , increasing the reaction-active zones, − and promoting the redox reaction kinetics. − For example, the carbon-based skeleton with N and/or P doping demonstrates an improved electronic conductivity and reaction kinetics. − Meanwhile, oxygen functional groups have been reported as catalysts for oxygen reduction , and hydrogen peroxide synthesis. , Furthermore, a common strategy to prepare the carbon materials with oxygen functional groups depends on the treatment by an acidic aqueous solution − or inheriting them from organic materials. , So far, MOF-derived composites have been rarely reported with abundant oxygen functional groups since most oxygen-containing groups decompose during the complex carbonization process. − …”