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Abstract We performed DFT calculations to investigate the role of solvent of the non-aqueous electrolytes for the oxygen reduction reaction (ORR) kinetics in Li-air batteries. The calculated results on structural, thermodynamic and vibrational properties revealed that dimethyl sulfoxide (DMSO) is the most stable solvent among DME, DMSO, and MeCN of non-aqueous electrolytes. The LiCF 3 SO 3 /DMSO electrolyte was primarily assumed to be the most favorable for ORR kinetics from the IR analysis. We calculated thermodynamic properties of the ORR reactions held during the formation of superoxide (O 2 −) ion and the sole discharge products lithium peroxide (Li 2 O 2), and lithium oxide (Li 2 O) to study the ORR kinetics of the stable salt LiCF 3 SO 3 with three solvents namely dimethoxyethane (DME), dimethyl sulfoxide (DMSO), and acetonitrile (MeCN). The thermodynamic properties of the ORR reaction signified the best role of LiCF 3 SO 3 /DMSO electrolyte compared to LiCF 3 SO 3 /DME and LiCF 3 SO 3 /MeCN both in the gas and solution (water) phases. Highlights • The role of solvent of non-aqueous electrolyte in Li-air batteries was studied theoretically. • The LiCF 3 SO 3 /DMSO electrolyte was primarily assumed to be the most favorable for ORR kinetics from the IR analysis. • The thermodynamic properties of the ORR reactions including the (O 2 −) ion and Li 2 O 2 and Li 2 O • Improved ORR kinetics was due to the key role of LiCF 3 SO 3 /DMSO electrolyte compared to LiCF 3 SO 3 /DME and LiCF 3 SO 3 /MeCN. [ABSTRACT FROM AUTHOR]

Observation of novel linear relationship between Δ G OOH and Δ E H suggests Δ E H as a simple descriptor for rational design of HER/ORR bifunctional graphyne materials. [Display omitted] The high cost and relative scarcity of platinum (Pt) restrict large-scale commercialization of fuel cells, which has spurred researchers to develop low-cost alternatives integrating with high hydrogen evolution reaction (HER) and oxygen reduction reaction (ORR) catalytic activity. Herein, we performed density functional theory (DFT) calculations to explore the electrocatalytic activity of graphyne nanotubes (GyNTs). Several GyNTs were found to be potential metal-free electrocatalysts, with both HER and ORR activity superior to Pt. Moreover, we revealed a linear relationship between the Gibbs free energy change of O 2 adsorption (Δ G OOH) and binding energy of H adsorption (Δ E H), which could be attributed to the fact that both the C O bond of OOH adsorption and the C H bond of H adsorption are single bonds. Therefore, Δ E H is proposed as a general descriptor for the rational design of bifunctional graphyne materials toward HERs and ORRs. Our findings provide a simple strategy for the rational design of bifunctional materials. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • MOFs-deriver N-doped CoC x /FeCo@C/rGO was synthesized as a catalyst for ORR. • The ORR activity of N-doped CoC x /FeCo@C/rGO was higher than that of the Pt/C. • The OER activity of N-doped CoC x /FeCo@C/rGO was higher than that of the RuO 2. • The synergistic effect of CoC x /FeCo and N-doped carbon results in the activity. Abstract Metal-organic framework derived materials have a great promise as non-precious metal-based electrocatalysts for large-scale applications of energy storage and transition devices with low-cost and high efficiency. Here, we report a high performance core-shell-structured nitrogen-doped CoC x /FeCo@C/reduced graphene oxide (rGO) hybrid, which is derived from Fe-doped Co 3 [Co(CN) 6 ] 2 MOFs, as bifunctional catalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). Structure characterizations show that the carbon shell of CoC x /FeCo and graphene support are bonded to each other, which offer a large surface area and stable anchoring sites for the CoC x /FeCo. Electrochemical tests show that N-doped CoC x /FeCo@C/rGO hybrid exhibits superior onset potential (1.0183 V vs RHE), half-wave potential (0.9653 V vs RHE), peak current intensity (0.9233 mA/cm−2) and long-term durability for ORR than those of Pt/C (onset potential, half-wave potential and peak current intensity are 1.0174 V and 0.9213 V, 0.8233 mA/cm−2, respectively) in 0.1 M KOH electrolyte. The overpotential of the hybrid for OER is only ∼390 mV at a current intensity of 10 mA/cm−2, which is close to that of the RuO 2. The excellent electrocatalytic properties of this hybrid make it a great potential to be substitute for precious-based catalysts for ORR and OER in fuel cells and water splitting. [ABSTRACT FROM AUTHOR]

The boron doped carbon nanomaterials that include in-plane B–C bonds at the local structure are considered as an efficient electrocatalyst for oxygen reduction reaction (ORR). However, a fundamental understanding about the electrocatalytic activity of out-of-plane B–C bonds remains unclear. Herein, we synthesize a boron nanosheet/reduced graphene oxide (B@rGO) heterostructure, where out-of-plane B–C chemical bonds are formed at the heterointerfaces, greatly improving the ORR activity. As verified by the combined experimental analyses and theoretical calculations, the ORR activity is boosted because the out-of-plane B–C chemical bonds contribute to the cleavage of O–O bond of O 2 * intermediate. The B@rGO heterostructure composite exhibits much higher ORR activity than those of respective boron and rGO nanosheets as demonstrated by half-wave potential, Tafel slope, electron transfer number, and electrochemical active area, achieving better durability and methanol tolerance than the commercial 20 wt% Pt/C catalyst. In this context, primary Zn–air battery, using the as-synthesized B@rGO heterostructure composite as metal-free electrocatalyst, delivers high peak power density of 131 mW cm−2 and specific capacity of 639.3 mAh g Zn −1. • Boron nanosheet/reduced graphene oxide heterostructure is constructed. • The out-of-plane B–C chemical bonds are formed at the heterointerfaces. • The ORR activity is boosted by the out-of-plane B–C bonds. • B@rGO heterostructure achieves high ORR activity and durability. • The Zn–air battery delivers a high power density of 131 mW cm−2. [ABSTRACT FROM AUTHOR]

• γ-graphyne nanoribbons are promising bifunctional electrocatalysts for ORR and HER. • Δ E H is a general energy descriptor for designing bifunctional electrocatalysts. • Light gradient boosting machine could predict electrocatalytic activities. Carbon-based metal free materials (CMFCs) as electrocatalysts have been a hot issue and are receiving growing attention. In this paper, we applied intensive density functional theory (DFT) calculations to study the electrocatalytic activities of γ-graphyne nanoribbons (γGyNRs) toward the oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER). Our results revealed γGyNRs to be excellent bifunctional CMFCs after functionalization by termination or N-doping at the edge to introduce proper spin densities. The scaling relationship analysis enhanced our earlier understanding that the binding strength of H atom (Δ E H) is a general descriptor for designing bifunctional electrocatalysts for HER and ORR. Further study revealed that the light gradient boosting machine is a promising machine learning algorithm to accurately predict the electrocatalytic activities of γGyNRs. Feature importance analysis suggested that the surrounding environment of the active site plays a more significant role than we previously anticipated. Overall, we suggest promising γGyNRs as HER and ORR bifunctional electrocatalysts for the first time and provide deeper insight into the reaction mechanism, which is beneficial for the rational design of novel CMFCs. [ABSTRACT FROM AUTHOR]