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Single‐atom catalysts (SACs) exhibit intriguing performance in electrocatalysis owing to their maximized atom utilizations and unique electronic structures, but effective anchoring metal atoms with defined coordination structure on hierarchical integrated electrode remain a challenge. Herein, a fast and facial flame‐assisted strategy is developed to construct oxygen‐coordinated SACs on integrated carbon nanotube (CNT) arrays with promising applications in electrocatalysis. Density functional theory calculations show that oxygen in carbon substrate imparts homogeneous sites for the efficient anchoring of metal atoms, thereby enabling SACs to disperse uniformly and firmly and thus bringing optimized activities. Moreover, the integrated CNT array with abundant oxygen‐containing groups is constructed and has been used as an efficient matrix for anchoring metal atoms (CNT‐O@M) via a flame‐assisted method. The as‐prepared CNT‐O@M (M = Co and Pt as typical examples) shows excellent activities in electrocatalytic oxygen reduction reaction and hydrogen evolution reaction with utilization of active site as high as 75.7%, which is superior to the reported SACs. Particularly, the performance of CNT‐O@M can maintain stably under various harsh conditions, showing a promising prospect in the long‐time applications. The methodology and concept proposed in this work could be extended to the synthesis of a variety of integrated SACs for efficient electrocatalysis. [ABSTRACT FROM AUTHOR]

Nitrogen doped carbon functionalized CoSe2 nanowires (CoSe2@N–C NWs), which act as potential oxygen evolution reaction (OER) catalysts with a large current density and high stability have been reported. Owing to the collaborative optimization of electrical conductivity, free adsorption energy and binding strength of OER intermediates, the prepared CoSe2@N–C NWs exhibit an enhanced 6.61-fold catalytic activity compared to the pristine CoSe2 NW electrode in 1.0 M KOH solution at the overpotential of 340 mV. [ABSTRACT FROM AUTHOR]

Facile engineering of transitional metal oxide nanoparticles (NPs) homogeneously anchored on graphitic carbon nitride (g‐C3N4) is very important. Herein, we develop a rapid and facile route to synthesize CuO NPs‐ and C, N‐codoped g‐C3N4 nanosheets grown on Ni foil (CuO/CN−C3N4/Ni‐f), derived from the oxidation‐pyrolysis of melamine‐entrapped Cu(II)‐MOF gel in the air. A detailed growth process for the hierarchical structure is studied. The obtained hierarchical structure without any binders used directly as an electrode only needs an overpotential of 223 mV to achieve a current density of 50 mA cm−2 in 0.5 M KOH, implying its highly efficient electrocatalytic activity. Notably, this material also exhibits strong long‐term durability. Free energy calculations show that the intrinsic origin of the outstanding activity is derived from sufficient exposure of active sites for CuO NPs anchored on the nanosheets and high N content. [ABSTRACT FROM AUTHOR]

B 4 C 12 achieves a rapid and stable CO 2 adsorption with a novel η3(O, C, O)-CO 2 configuration, and a small limiting potential for CO2RR producing HCOOH associating with suppressed HER. [Display omitted] The electrochemical reduction of CO 2 (CO2RR) to formic acid (HCOOH) is a promising approach to harness renewable energy for the production of value-added chemicals and contribute to carbon cycling. The search for cost-effective and efficient metal-free electrocatalysts is critical for realizing industrial applications. However, limited literature is available on this topic, primarily because the significant challenge of efficiently activating inert CO 2 remains unresolved. In this study, we have designed and applied a novel boron carbide (B 4 C 12) monolayered cage as an electrocatalyst for CO2RR to produce HCOOH. B 4 C 12 exhibits exceptional electronic, dynamic, and thermodynamic stability. Through comprehensive density functional theory computations, we have observed that B 4 C 12 rapidly and stably adsorbs CO 2 in a unique η3(O, C, O)-CO 2 configuration, resulting in excellent CO2RR activity with a low limiting potential (–0.38 V) and suppressed hydrogen evolution reaction. Our mechanistic investigations reveal that B 4 C 12 donates electrons to facilitate the bending of CO 2 , anchoring it onto the curved surface effectively. Additionally, the C atom in the η3(O, C, O)-CO 2 configuration attracts H+ + e− pairs through its active p electron, leading to the observed low limiting potential. This study not only successfully designs a novel class of metal-free electrocatalysts but also provides a promising strategy for advancing CO2RR research in the future. [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]

[Display omitted] • γ-graphdiyne nanoribbons are potential bifunctional CMFCs for ORR and HER after edge functionalization. • sp-N doping can effectively boost the ORR and HER performance of inert γGDyNRs. • Light gradient boosting machine could predict electrocatalytic activities. Graphyne materials have shown promising advantages for fabrication of carbon-based, metal-free catalysts (CMFCs) in the electrocatalytic field. Herein, we report functionalized γ-graphdiyne nanoribbons (γGDyNRs) by edge termination or N doping as potential bifunctional CMFCs for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) via intensive density functional theory (DFT) simulations. It is revealed that sp-N doping (sandwiched by two sp-C) at the inner location and sp2-N doping near the edge can effectively boost the ORR and HER performance of inert γGDyNRs. Our results further demonstrate that sp2-N can play a principal role, especially when at the edge of γGDY; this effect was not addressed in earlier experimental and theoretical work. We also built a machine learning model for predicting bifunctional activities using a light gradient boosting machine. Feature importance analysis shows that the distance between adsorption site and the closest atom to it and the atomic charge of adsorption site are the most important features in determining the activities. Our work not only identifies γGDyNRs as promising alternative catalysts to Pt, but also benefits the rational design of novel CMFCs with high efficiency. [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]

[Display omitted] • Electrocatalytic Re nanoflowers (Re NFs) were grown on a carbon cloth (CC) substrate. • Optimal synthesis and growth mechanism of Re NFs on CC were validated. • Density functional theory (DFT) calculations determined intrinsic HER activity of Re. • Hydrogen evolution reaction (HER) activity of Re in different pH environments was evaluated. • ReNF@CC performed eminent HER activities with significantly reduced overpotentials. The hydrogen evolution reaction (HER) is one of the primary routes for clean hydrogen energy production to replace fossil fuels. However, the lack of cost-effective electrocatalysts hinders its practical implementation. Re, which is considerably less expensive than Pt, has recently emerged as an electrocatalyst owing to its high HER activity over a wide pH range. However, HER processes of Re have been studied primarily through spectroscopy, with little theoretical interpretation to explain the intrinsic HER activity of Re. Additionally, it is necessary to develop antioxidative Re electrocatalysts to prevent hydrogen intercalation, and to suppress catalyst aggregation to ensure long-term stability. In this work, a theoretical analysis was first conducted to investigate the free energy of each HER intermediate and demonstrate high performance of Re. Then, a novel free-standing electrocatalyst consisting of Re nanoflowers (NFs) grown in-situ on a carbon cloth (CC) was synthesized (ReNF@CC) via a hydrothermal method followed by thermal annealing. The Re NFs homogeneously grown on the CC surface effectively suppressed self-aggregation to preserve abundant active sites, and the direct coupling of Re NFs enhanced the conductivity and physical/electrochemical stability to prevent their detachment from the CC during operation. A high HER performance was obtained with low overpotentials of 103, 115, and 75 mV at 10 mA cm−2 in 0.5 M H 2 SO 4 , 1 M PBS, and 1 M KOH, respectively; additionally, a superior durability with respect to commercial Pt/C was achieved. Overall, this study offers a versatile and universal strategy for highly efficient water electrolysis in different media. [ABSTRACT FROM AUTHOR]

The sluggish oxygen evolution reaction (OER) limits the efficiency of overall water splitting, which thereby hinders hydrogen evolution reaction (HER). Here, we demonstrate a bifunctional CoNiP nanosheet integrated electrode (CoNiP-NIE) to boost HER and replace OER by 5-hydroxymethylfurfural oxidation reaction (HMFOR) to obtain high-valued 2,5-furandicarboxylic acid (FDCA). The as-developed CoNiP-NIE exhibits a constant high Faradaic efficiency more than 82% for HMFOR in a wide potential from 1.40 V to 1.70 V vs. RHE, which stand at the top level among the reported electrocatalysts. Moreover, the low overpotential for HER further indicates its high efficiency in the H 2 generation. Based on the bifunctional activity of CoNiP, an electrochemical hydrogen evolution coupled with biomass oxidation device is constructed, which delivers lower voltage (1.46 V) for anode oxidation and higher evolution rate of H 2 (41.2 L h−1 m−2) than water splitting (1.76 V, 16.1 L h−1 m−2). We report a bifunctional CoNiP nanosheet integrated electrode by facile ion etching and subsequent phosphidation process, which shows promising activity for HMFOR and HER simultaneously. This work thus could provide a successful paradigm for rational design bifunctional electrocatalysts for highly efficient hydrogen production coupled with biomass oxidation. [Display omitted] • The CoNiP-NIE exhibits high FE FDCA in a wide potential from 1.40 to 1.70 V vs. RHE. • An EHCO device based on bifunctional CoNiP-NIE enhances the evolution rate of H 2. • CoNiP displays moderate desorption for FDCA and enhanced electrical conductivity. [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]

• Few-layered ReSe 2 nanoflakes are vertically arranged on rGO. • Mechanism of vertical growth of ReSe 2 on rGO is clarified by DFT calculation. • Plentiful exposed edges/corners on ReSe 2 facilitate the generation of active sites for electrocatalysis. • Improved electrical conductivity and electrochemical stability of ReSe 2 are realized after hybrid with rGO. • Prominent HER performance is measured with a low overpotential and small Tafel slope. Hydrogen evolution reaction (HER) by water splitting has made a significant contribution to producing large amounts of hydrogen gas as the next generation fuel. Development of highly efficient, economically viable, and electrochemically stable HER electrocatalysts has accordingly become a prerequisite for practical implementation of large scale water electrolysis. Mono/few-layered transition metal dichalcogenide (TMD) based HER-electrocatalysts have recently garnered great interest due to their diverse tunable electrochemical properties. However, they still face intrinsic limitations such as self-aggregation, rare active sites, high electrical resistance, and long-term electrochemical instability. To tackle these challenges, we designed and synthesized a novel electrocatalyst comprising active site-rich rhenium diselenide (ReSe 2) nanoflakes perpendicularly anchored on a reduced graphene oxide (rGO) nanosheet support via a facile one-step hydrothermal synthesis. The rGO support provides a growing platform for few-layered ReSe 2 nanoflakes while facilitating plentiful exposure of edge/corner sites of ReSe 2 , highly desirable for maximizing the catalytic activity of ReSe 2 @rGO. The synthesized ReSe 2 @rGO exhibits a low overpotential of 145.3 mV at a current density of 10 mA·cm−2 with a Tafel slope of 40.7 mV·dec−1 for the HER process due to the synergistic combination of high surface density of unsaturated coordination sites, remarkably accelerated electron transfer, and enhanced electrochemical stability. This outcome suggests using structurally regulated hybridization of TMDs and graphene as a platform toolkit for developing high performance HER catalysts. [ABSTRACT FROM AUTHOR]