Chemical state of surrounding iron species affects the activity of Fe-Nx for electrocatalytic oxygen reduction

The design on synthesizing a sturdy, low‐cost, clean, and sustainable electrocatalyst, as well as achieving high performance with low overpotential and good durability toward water splitting, is fairly vital in environmental and energy‐related subject. Herein, for the first time the growth of sulfur (S) defect engineered self‐supporting array electrode composed of metallic Re and ReS2 nanosheets on carbon cloth (referred as Re/ReS2/CC) via a facile hydrothermal method and the following thermal treatment with H2/N2 flow is reported. It is expected that, for example, the as‐prepared Re/ReS2‐7H/CC for the electrocatalytic hydrogen evolution reaction (HER) under acidic medium affords a quite low overpotential of 42 mV to achieve a current density of 10 mA cm−2 and a very small Tafel slope of 36 mV decade−1, which are comparable to some of the promising HER catalysts. Furthermore, in the two‐electrode system, a small cell voltage of 1.30 V is recorded under alkaline condition. Characterizations and density functional theory results expound that the introduced S defects in Re/ReS2‐7H/CC can offer abundant active sites to advantageously capture electron, enhance the electron transport capacity, and weaken the adsorption free energy of H* at the active sites, being responsible for its superior electrocatalytic performance.

Section: Figuresupporting

confidence: 68%

“…The Tafel slopes are 36, 81, and 21 mV decade −1 for Re/ReS 2 ‐7H, ReS 2 and Pt/C, suggesting that the electron transfer efficiency is probably the rate‐determining step for ORR. [ 21a ]…”

Section: Figurementioning

confidence: 99%

Hydrogen‐Etched Bifunctional Sulfur‐Defect‐Rich ReS₂/CC Electrocatalyst for Highly Efficient HER and OER

Pang

Niu

et al. 2020

“…In order to clarify whether Co–N x exists in CoNC‐NB2, the conventional poisoning experiment was carried out using SCN − ion to block the Co–N x sites in catalyzing ORR. [ 20 ] Considering the instability of SCN − ions in KOH solution, the ORR activity was measured in O 2 ‐saturated 0.1 m HClO 4 with or without 0.01 m NaSCN. It can be seen in Figure 2f that the ORR activity of CoNC‐NB2 decreases significantly in the presence of SCN − .…”

Section: Resultsmentioning

confidence: 99%

Self‐Catalyzed Growth of Co–N–C Nanobrushes for Efficient Rechargeable Zn–Air Batteries

Luo

Jiang

Niu

et al. 2020

Self Cite

have been considered as attractive alternatives in next-generation energy storage systems due to their high energy density, safety, and environmental friendliness. [2] The big challenge for this technique is the development of highly efficient and stable air electrode. It requires highly active electrocatalysts for both oxygen reduction reactions (ORR) and oxygen evolution reactions (OER) to overcome sluggish kinetics for four electron transfer processes and significantly reduce the reaction overpotentials. [3] Although noblemetal-based catalysts, such as platinum (Pt), ruthenium (Ru), iridium (Ir), and their alloys, are the best-known oxygen electrocatalysts, their commercialization are greatly hindered by their reserves, high cost, and still insufficient catalytic performance for bifunctional oxygen reactions. [4] Over the past few years, much efforts have been devoted to developing non-noble metal bifunctional electrocatalysts, such as transition metal sulfide/oxides, [5] nitrides, [6] carbon materials, [7] and so on. [8] Among these catalysts, the transitional metal-containing N-doped carbon materials (M-N-C, M = Fe, Co, Ni, etc.) have attracted intense attention. The transition metals in such catalysts greatly enhance the graphitization and thus electrical conductivity of carbon matrix, which provide them the better protection in turn from corrosion and aggregation during the electrochemical reactions. [4b,9] Furthermore, the interactions and synergistic effects between metal species and N-doped carbon species enhance the intrinsic electrochemical activity for ORR and OER by electronically modulating the charge distribution on active sites and thus the adsorption/ desorption of O 2 and intermediates. [4c,10] M-N-C materials are usually obtained from the direct pyrolysis of precursors, such as transition metal macrocycles/ polymers (e.g., porphyrins and phthalocyanines) or the mixture of nitrogen-rich organic compounds and transition-metal salts, which commonly gives the inhomogeneous microstructures and uncontrollable agglomeration of active components due to the high reactivity of transition metal at high-temperature. Such structure could lead to the insufficient exposure of active sites as well as poor electron and mass transport. [11] 1D nanostructures such as nanotubes, [12] nanofibers, [13] nanorod, [14] etc., were thus introduced to improve the electron transportation. The shortcoming is the insufficient surface area for accommodating Highly efficient and stable bifunctional electrocatalysts for oxygen reduction and evolution are essential for aqueous rechargeable Zn-air batteries, which require highly active sites as well as delicate structural design for increasing effective active sites and facilitating mass/electron transfer. Herein, a scalable and facile self-catalyzed growth strategy is developed to integrate highly active Co-N-C sites with 3D brush-like nanostructure, achieving Co-N-C nanobrushes with Co,N-codoped carbon nanotube branches grown on Co,Ncodoped nanoparticle assembled na...

“…Density functional theory (DFT) calculations are performed to get further insights on the intrinsic interactions between FeN 4 moieties and modified Fe 3 C‐Fe species . The model structures including bare FeN 4 moiety and simplified metallic Fe‐atoms modifying FeN 4 systems are shown in Figure S13 (Supporting Information) . The adsorption energy value of O 2 ( E ad ) on various models plays a decisive role in ORR.…”

Section: Resultsmentioning

confidence: 99%

Atomic‐Level Fe‐N‐C Coupled with Fe₃C‐Fe Nanocomposites in Carbon Matrixes as High‐Efficiency Bifunctional Oxygen Catalysts

Sun

Wei

et al. 2019

100