Identifying the Key Role of Pyridinic‐N–Co Bonding in Synergistic Electrocatalysis for Reversible ORR/OER

Abstract

For many regenerative electrochemical energy-conversion systems, hybrid electrocatalysts comprising transition metal (TM) oxides and heteroatom-doped (e.g., nitrogen-doped) carbonaceous materials are promising bifunctional oxygen reduction reaction/oxygen evolution reaction electrocatalysts, whose enhanced electrocatalytic activities are attributed to the synergistic effect originated from the TM-N-C active sites. However, it is still ambiguous which configuration of nitrogen dopants, either pyridinic or pyrrolic N, when bonded to the TM in oxides, predominately contributes to the synergistic effect. Herein, an innovative strategy based on laser irradiation is described to controllably tune the relative concentrations of pyridinic and pyrrolic nitrogen dopants in the hybrid catalyst, i.e., NiCo O NPs/N-doped mesoporous graphene. Comparative studies reveal the dominant role of pyridinic-NCo bonding, instead of pyrrolic-N bonding, in synergistically promoting reversible oxygen electrocatalysis. Moreover, density functional theory calculations provide deep insights into the corresponding synergistic mechanism. The optimized hybrid, NiCo/NLG-270, manifests outstanding reversible oxygen electrocatalytic activities, leading to an overpotential different ΔE among the lowest value for highly efficient bifunctional catalysts. In a practical reversible Zn-air battery, NiCo/NLG-270 exhibits superior charge/discharge performance and long-term durability compared to the noble metal electrocatalysts.

A Facile Synthesis of FeCo Nanoparticles Encapsulated in Hierarchical N‐Doped Carbon Nanotube/Nanofiber Hybrids for Overall Water Splitting

“…It is interesting to note here that the samples with CNTs i. e. FeCo@NC‐11 and FeCo@NC‐12, have significant coordination of pyridinic N with the metal (Figure a) with highest proportion of N pyridinc /N graphitic of 1.74 for the FeCo@NC‐12 sample (Table S5 in SI). Earlier reports suggest that FeCo alloy with appropriate doping level of Co catalyze the formation of pyridinic N . The substantial presence of pyridinic N and its binding with metal to form active M−N‐C structure is also confirmed by the XPS spectra of Co 2p and Fe 2p in Figure (b–c), respectively.…”

Heterostructures Composed of N‐Doped Carbon Nanotubes Encapsulating Cobalt and β‐Mo2C Nanoparticles as Bifunctional Electrodes for Water Splitting

“…High durability is an important criterion for an efficient electrocatalyst. [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33][34] To unveil the electronic interactions between b-Mo 2 C, Co, and N-CNTs,w es ystematically performed and compared DFT calculations on the adsorption free energy of H* (DG H* represents an adsorption site) of several models,i ncluding CNTs,N -CNTs,C o@N-CNTs,M o 2 C@N-CNTs,a nd Co/b-Mo 2 C@N-CNTs,d uring the HER (see Figure S12). Accelerated LSV was also conducted continuously for 1000 cycles,and the overpotential of Co/b-Mo 2 C@N-CNTs only increased by about 13 mV at j 10 (see Figure S11).…”

“…[11][12][13] Notably,t he combination of Mo 2 Cw ith transition metals can effectively reduce the amount of unoccupied dorbitals of Mo to further enhance the HER activity,o wing to the electron-rich nature of transition metals.A lthough Mo 2 C-based materials with superior HER properties have been widely reported, their low OER activity has become am ajor obstacle for overall water splitting.T od ate,t he investigation of Mo 2 C-based electrocatalysts for OER has been limited. [16] Cobalt-based hybrids can greatly improve the OER catalytic activity of materials,i ncluding Co-N, [17] Co-Pi (Pi = inorganic phosphate), [18] NiCo 2 O 4 , [19] NiCo alloy, [20] and others. [15] Thea bove results suggest that the development of an efficient Mo 2 C-based electrocatalyst to create aw ater electrolyzer is still ac onsiderable challenge.…”

“…In this context, Yu and co-workers synthesized Ni/Mo 2 Cn anorods coated with apolydopamine hybrid, which required an overpotential (h 10 ) of over 368 mV to reach ac urrent density of 10 mA cm À2 , [14] and Luo and co-workers reported aMo 2 C/carbon hybrid that required an h 10 value over 500 mV. [16] Cobalt-based hybrids can greatly improve the OER catalytic activity of materials,i ncluding Co-N, [17] Co-Pi (Pi = inorganic phosphate), [18] NiCo 2 O 4 , [19] NiCo alloy, [20] and others. [16] Cobalt-based hybrids can greatly improve the OER catalytic activity of materials,i ncluding Co-N, [17] Co-Pi (Pi = inorganic phosphate), [18] NiCo 2 O 4 , [19] NiCo alloy, [20] and others.…”

Engineering the Interface of Carbon Electrocatalysts at the Triple Point for Enhanced Oxygen Reduction Reaction

“…[11d, 27] Interfacial engineering of heteroatom doping to create surface-enriched active sites is an efficient methodt oi mprove the ORR activity.T he active sites formed on the catalyst surface are in directc ontact with the three-phase reactants such as the electrolyte, the oxygen bubbles and the catalyst's active sites. [29] Some research reports claim that pyridinic-Ns ites play an important role in deciding the onset potential, while the amounto fn itrogen determines the saturated current density. [28] Amongt hese different dopants, Fe in combination with N-doping has been regarded as an efficient catalytic site and has been widely applied.…”