Reversible Hydrogen Electrode Research Articles

Engineering spin-dependent catalysts: chiral covalent organic frameworks with tunable electroactivity for electrochemical oxygen evolution.

The chiral-induced spin selectivity (CISS) effect offers promising prospects for spintronics, yet designing chiral materials that enable efficient spin-polarized electron transport remains challenging. Here, we report the utility of covalent organic frameworks (COFs) in manipulating electron spin for spin-dependent catalysis via CISS. This enables us to design and synthesize three three-dimensional chiral COFs (CCOFs) with tunable electroactivity and spin-electron conductivity through imine condensations of enantiopure 1,1'-binaphthol-derived tetraaldehyde and tetraamines derived from 1,4-benzenediamine, pyrene, or tetrathiafulvalene skeletons. The CISS effect of CCOFs is verified by magnetic conductive atomic force microscopy. Compared with their achiral analogs, these CCOFs serve as efficient spin filters, reducing the overpotential of oxygen evolution and improving the Tafel slope. Particularly, the diarylamine-based CCOF showed a low overpotential of 430mV (vs reversible hydrogen electrode) at 10mAcm-2 with long-term stability comparable to the commercial RuO2. This enhanced spin-dependent OER activity stems from its excellent redox-activity, good electron conductivity and effective suppression effect on the formation of H2O2 byproducts.

Boosting synergistic hole separation and transfer in the TiO2-MXene photoanode by depositing amorphous NiOOH/CoOOH cocatalysts

The efficient separation and transport of photogenerated charge carriers within the photoanode are pivotal for achieving high-performance photoelectrochemical (PEC) water splitting. In this study, TiO2-MXene nanowire arrays (NWAs) adorned with amorphous CoOOH/NiOOH (CN) were fabricated using hydrothermal and photo-assisted electrodeposition techniques. TiO2-MXene-CN NWAs demonstrated a photocurrent density of 1.51 mA/cm2 at 1.23 V versus the reversible hydrogen electrode (vs. RHE), which is 1.46 times and 2.79 times that of TiO2-CN and TiO2, respectively. Electrochemical impedance spectroscopy, photoluminescence, time-resolved photoluminescence, and Mott-Schottky analysis unveiled that the incorporation of MXene and CN substantially augmented the separation of photogenerated electron-hole pairs and efficient charge carrier utilization. Furthermore, the loading of MXene-CN layers ameliorated the light absorption performance of bare TiO2 NWAs. This work provides valuable insights for the design of photoelectrodes employing wide-bandgap materials.

Simultaneously Tuning Charge Separation and Surface Reaction Kinetics on ZnIn2S4 Photoanode by P-Doping for Highly Efficient Photoelectrochemical Water Splitting and Urea Oxidation

ZnIn2S4 nanosheets are a promising photoanode for driving photoelectrochemical (PEC) hydrogen fuel production; nevertheless, poor charge separation and sluggish surface reaction kinetics hinder its PEC performance to an extreme degree. Herein, a facile element doping strategy (i.e., P element) was developed to obtain the desired photoanode. As a result, the ZnIn2S4-P (ZIS-P5) photoanode exhibits a remarkable photocurrent density of 1.66 mA cm−2 at 1.23 V versus a reversible hydrogen electrode (VRHE) and a much lower onset potential of 0.12 V vs. RHE for water oxidation. Careful electrochemical analysis confirms that the P doping and sulfur vacancies (Sv) not only facilitate the hole transfer, but also boost surface reaction kinetics. Finally, the “killing two birds with one stone” goal can be achieved. Moreover, the optimized photoanode also presents high PEC performance for urea oxidation, obtaining a photocurrent density of 4.13 mA cm−2 at 1.23 V vs. RHE. This work provides an eco-friendly, simple and effective method to realize highly efficient solar-to-hydrogen conversion.

Engineering CoO/B heterojunction electrocatalysts for boosting electrocatalytic nitrate reduction to ammonia

Electrocatalytic nitrate reduction to ammonia represents a one-stone-two-birds approach for mitigating nitrate pollution and large-scale ammonia production. However, due to its multiple-electron process, it faces challenges regarding unsatisfactory Faraday efficiency (FE) and ammonia yield rate. Herein, a novel heterojunction electrocatalyst with sub-nanometric cobaltous oxide (CoO) decorated boron (B) nanosheets for electrocatalytic nitrate reduction (NO3RR) is first presented as an efficient electrocatalyst. The CoO/B heterojunction electrocatalyst exhibits a noteworthy NO3RR performance with an ammonia FE and yield rate of 95.41 % and 29.42 mg h-1 mgcat-1, respectively, in alkaline media at −0.4 V vs. reversible hydrogen electrode (RHE), surpassing CoO and B catalysts. Results demonstrated that the synergistic effect of CoO and B enhances the adsorption and activation of NO3−, lowers the formation energy of *NOH and provides sufficient active hydrogen to facilitate hydrogenation, thereby enhancing NO3RR performance. This work presents a novel approach for constructing cost-effective and high-performance NO3RR heterojunction electrocatalysts.

Green synthesis of Cu-based metal organic framework for electrochemical CO2 conversion into formic acid

Metal-organic frameworks (MOFs) show promising amendments for the remediation of CO2. As the literature reports considerable progress in the electrochemical reduction of CO2, this work focuses on facile green synthesis of metal-organic framework and yields formic acid. The green synthesis MOF involved the use of an aqueous water-based solvent for synthesis, then compared with the conventional hydrothermal method of synthesis using N, N-Dimethylformamide (DMF), and was studied for electrochemical reduction of CO2. Green synthesis of copper benzene tricarboxylic acid (Cu BTC) and conventional synthesis of Cu BTC were characterized by XRD (X-ray diffraction), SEM (Scanning electron microscopy), TEM (Transition electron microscopy), FT-IR (Fourier transform infrared), and XPS (X-ray photoelectron spectroscopy). The performance of the green synthesis of Cu BTC resulted in the achievement of the highest FE (Faradic efficiency) of formic acid of 88 %, at - 0.6 V (vs. Reversible hydrogen electrode (RHE)) in 0.5 M Potassium chloride (KCl) electrolyte.

Manipulation of Oxygen Species on an Antimony-Modified Copper Surface to Tune the Product Selectivity in CO2 Electroreduction.

Rational regulation of the electrochemical CO2 reduction reaction (CO2RR) pathway to produce desired products is particularly interesting, yet designing economical and robust catalysts is crucial. Here, we report an antimony-modified copper (CuSb) catalyst capable of selectively producing both CO and multicarbon (C2+) products in the CO2RR. At a current density of 0.3 A/cm2, the faradaic efficiency (FE) of CO was as high as 98.2% with a potential of -0.6 V vs reversible hydrogen electrode (RHE). When the current density increased to 1.1 A/cm2 at -1.1 V vs RHE, the primary products shifted to C2+ compounds with a FE of 75.6%. Experimental and theoretical studies indicate that tuning the potential could manipulate the oxygen species on the CuSb surface, which determined the product selectivity in the CO2RR. At a more positive potential, the existence of oxygen species facilitates the potential-limiting step involving *COOH formation and reduces the adsorption of *CO intermediates, thereby promoting CO production. At a more negative potential, the localized high CO concentration coupled with the enhanced adsorption of *CO intermediates due to Sb incorporation facilitates C-C coupling and deep hydrogenation processes, resulting in an increased C2+ selectivity.

Electrocatalytic reduction of nitrate to ammonia over activated carbon-supported copper-iron bimetallic catalyst synthesized by hydrothermal co-precipitation method

Ammonia synthesis via electrocatalytic reduction of nitrate is a promising approach for green ammonia production. However, this process limited by multiple reaction pathways and NO3− adsorption over electrocatalyst surface. Herein, copper-iron bimetallic catalysts with different atom ratios of Cu/Fe (Cu/Fe = 10/0, 7/3, 5/5, 3/7 and 0/10) and activated carbon as supporter (CuFeOx/AC) were synthesized through hydrothermal co-precipitation method for catalytic reduction of nitrate. Synergistic effects between the Cu and Fe were observed in the copper-iron bimetallic catalysts and an appropriate atom proportion of Cu/Fe was benefit to accelerate the adsorption and electrocatalytic kinetics of nitrate reduction to *NO2 and *NO2 hydrogenation to·NH3 through electron redistribution. The catalyst of 7Cu3FeOx/AC presented the best catalytic performance in nitrogen electroreduction reaction for ammonia synthesis, with an NH3 yield rate of 2091 μg h−1 mgcat−1 and a faradaic efficiency of 76 % at −0.8 V vs. reversible hydrogen electrode. The 7Cu3FeOx/AC also exhibited excellent cycle ability and long-term durability whose NH3 yield rates maintained as high as 1476 and 2326 μg h−1 mgcat−1 after 9 cycles and 10 h durability measurement, respectively. The nitrate reduction behavior over 7Cu3FeOx/AC proceeded with a series of deoxygenation reactions as follows: NO3− → *NO3 → *NO2 → *NO → *NOH → *NH2OH →·NH3. With the above excellent properties, the 7Cu3FeOx/AC may prove to be a promising electrocatalyst for ammonia synthesis via nitrogen electroreduction reaction.

Construction of high‐loading WO3‐x sub‐nanometer clusters via orderly‐anchored top–down strategy boost acidic hydrogen evolution

AbstractExploring a simple, rapid, and scalable synthesis method for the synthesis of high loading nonprecious metal sub‐nanometer clusters (SNCs) electrocatalysts is one of the most promising endeavors today. Herein, an orderly‐anchored top–down strategy is proposed for fabricating a new type of high loading WO3‐x SNCs on O‐functional group‐modified Ketjen black (WO3‐x‐C(O)) to balance the high loading (49.29 wt.%) and sub‐nanometer size. By optimizing the vacancy number, WO2.71‐C(O) has extremely large electrochemically active surface area (402 m2 g−1) and high turnover frequency value of 1.722 s−1 at −50 mV (vs. reversible hydrogen electrode). The overpotential of WO2.71‐C(O) reaches 22 mV at a current density of 10 mA cm−2, which is significantly better than the commercial Pt/C level (32 mV), achieving a breakthrough in the hydrogen evolution reaction (HER) catalytic activity of nonprecious metals in acidic environment. Theoretical calculations and in situ characterization show that this material allows for the enrichment of reactants (H*) and the optimization of intermediate adsorption, which leads to the enhancement of acidic HER catalytic activity.

Tandem Effect Promotes MXene‐Supported Dual‐Site Janus Nanoparticles for High‐Efficiency Nitrate Reduction to Ammonia and Energy Output through Zn‐Nitrate Battery

AbstractElectrocatalytic nitrate reduction reaction (NO3RR) can convert nitrate contaminants into ammonia with higher added value. However, due to the NO3RR involving complex multi‐electron reactions, there is an urgent need to develop efficient electrocatalysts. Herein, CoCu Janus nanoparticles loaded on Ti3C2Tx MXene (CoCu‐Ti3C2Tx) is synthesized via the combination of molten salt etching and galvanic replacement strategy. The tandem catalysis of CoCu Janus NPs can maintain the balance between nitrogenous intermediates and active hydrogen (Hads). CoCu‐Ti3C2Tx exhibits a high NH3 yield of 8.08 mg h−1 mgcat.−1 and a satisfactory Faradaic efficiency of 93.6% at −0.7 V versus reversible hydrogen electrode (RHE). The Zn‐NO3− battery assembled with CoCu‐Ti3C2Tx shows an excellent power density of 10.33 mW cm−2, an NH3 yield of 1.52 mg h−1 mgcat.−1 and a Faradaic efficiency of 95.3% at 10 mA cm−2, which enables the simultaneous elimination of nitrate pollutants, ammonia production, and energy supply. Moreover, a series of verification experiments and density functional theory calculation are combined to reveal the reaction path and tandem catalytic mechanism. This work not only provides a new inspiration for the design of tandem catalysts but also promotes the development of Zn‐nitrate battery.

Atomic Defects Engineering Boosts Urea Synthesis toward Carbon Dioxide and Nitrate Coelectroreduction.

The atomic defect engineering could feasibly decorate the chemical behaviors of reaction intermediates to regulate catalytic performance. Herein, we created oxygen vacancies on the surface of In(OH)3 nanobelts for efficient urea electrosynthesis. When the oxygen vacancies were constructed on the surface of the In(OH)3 nanobelts, the faradaic efficiency for urea reached 80.1%, which is 2.9 times higher than that (20.7%) of the pristine In(OH)3 nanobelts. At -0.8 V versus reversible hydrogen electrode, In(OH)3 nanobelts with abundant oxygen vacancies exhibited partial current density for urea of -18.8 mA cm-2. Such a value represents the highest activity for urea electrosynthesis among recent reports. Density functional theory calculations suggested that the unsaturated In sites adjacent to oxygen defects helped to optimize the adsorbed configurations of key intermediates, promoting both the C-N coupling and the activation of the adsorbed CO2NH2 intermediate. In-situ spectroscopy measurements further validated the promotional effect of the oxygen vacancies on urea electrosynthesis.

Engineering superhydrophilic Ni-Se-P on Ni-Co nanosheets-nanocones arrays for enhanced hydrogen production assisted by hydrazine oxidation reaction

The production of hydrogen gas as an environmentally friendly and emission-free fuel source, has emerged as the preeminent substitute for traditional fossil fuels. The demand for a viable and low-cost substitute of the anodic Oxygen Evolution Reaction (OER) in hydrogen gas production has led researchers to explore the Hydrazine Oxidation Reaction (HzOR), aiming to reduce overpotential. In this study, we present the synthesis of a NiSeP@NiCo/Cu electrocatalyst via electrodeposition method, offering precise control over parameter adjustments and an affordable price. The binder-free nanosheet structure of this electrocatalyst demonstrates improved performance in water electrolysis, resulting in potentials of −40 and −134 mV vs. Reversible Hydrogen Electrode (RHE) for Hydrogen Evolution Reaction (HER) and 0.041 and 0.194 V (vs. RHE) for HzOR (i = 10 and 100 mA.cm−2). The electrode has excellent features, including active electrochemical surface, synergistic effects among the elements, high stability, super-hydrophilicity and super-aerophobicity. The Bi-functional performance of electrode was tested in a two-electrode set for HER/HzOR, the cell voltage required to reach current densities of 10 and 100 mA.cm−2 were determined as 0.071 and 0.298 V respectively. On the whole, this work presents the excellent capabilities of the synthesized electrode (NiSeP@NiCo/Cu) for hydrogen gas production.

Exploring the synergistically enhanced activity of novel α-MnSe/ppy composite for superior OER catalyst in alkaline medium

The extremely slow kinetics of the water-splitting process stymies the synthesis of hydrogen (H2) from water. To comprehend the main obstacle to the oxygen evolution reaction (OER), it is also necessary to enhance the development of efficient OER electrocatalysts. In this work, manganese selenide with polypyrrole heterostructure is synthesized, described, and electrochemically assessed as an effectiveelectrocatalystfor OER. The novel synthesized materialis characterizedusing a variety of techniques, including scanning electron microscopy (SEM), powder x-ray diffraction (PXRD), transmission electron microscopy (TEM) etc. The unique α-MnSe/ppy composite catalyst is shown to be exceedingly efficient, starting the OER at an astoundingly low voltage of 168 mV (vs. reversible hydrogen electrode [RHE]) at 10 mA cm−2, with a tafel slope of 67 mV dec-1. Also, operando UV–Vis spectro-electrochemical studies give an insight towards the intermediate species formed during the OER catalysis. Under similar electrochemical conditions, the α-MnSe/ppy electrocatalyst outperforms its α-MnSe and ppy counterparts for OER in an aqueous KOH (1.0 M) solution. These results surpass benchmark electrocatalysts made of Mn and rare earth metals. With this invention, a desired non-noble metal is made available that works excellently as an OER electrocatalyst.

Atomically dispersed nickel-bismuth dual-atom sites for high rate electrochemical CO2 reduction

We report a diatomic-site catalyst configuration constituted by Ni-N3 and Bi-N4 embedded in ultrathin nitrogenated carbon nanosheets (Ni/Bi-N-C) which showed dramatically improved activity and selectivity for the conversion of CO2 to CO. Specifically, the catalyst exhibited high CO Faradaic efficiency (FECO) of above 90 % over a wide potential window from −0.76 to −2.22 versus reversible hydrogen electrode with the maximum CO partial current density up to 312 mA cm−2 in a flow cell, and coupled with robust durability. Ni/Bi-N-C-based membrane electrode assembly (MEA) device presented ultrahigh FECO of 95.7 % at 750 mA and over 100 h of continuous operation without decay under constant current density of 100 mA cm−2. Mechanistic studies and density functional theory calculations reveal that regulating the CO2RR catalytic performance via nearby Ni and Bi active sites can potentially break the activity benchmark of the single metal counterparts because the neighboring Ni and Bi active sites work in synergy to decrease the reaction barrier for the formation of *COOH and desorption of *CO. This work presents an efficient combination of two metal atomic sites which was designed by optimizing the interaction between the atomic sites and key reaction intermediates, resulting in the high-rate electrocatalytic CO2 reduction.

Dual Polarization of Ni Sites at VOx-Ni3N Interface Boosts Ethanol Oxidation Reaction.

Substituting thermodynamically favorable ethanol oxidation reaction (EOR) for oxygen evolution reaction (OER) engenders high-efficiency hydrogen production and generates high value-added products as well. However, the main obstacles have been the low activity and the absence of an explicit catalytic mechanism. Herein, a heterostructure composed of amorphous vanadium oxide and crystalline nickel nitride (VOx-Ni3N) is developed. The heterostructure immensely boosts the EOR process, achieving the current density of 50mA cm-2 at the low potential of 1.38V versus reversible hydrogen electrode (RHE), far surpassing the sluggish OER (1.65V vs RHE). Electrochemical impedance spectroscopy indicates that the as-fabricated heterostructure can promote the adsorption of OH- and the generation of the reactive species (O*). Theoretical calculations further outline the dual polarization of the Ni site at the interface, specifically the asymmetric charge redistribution (interfacial polarization) and in-plane polarization. Consequently, the dual polarization modulates the d-band center, which in turn regulates the adsorption/desorption strength of key reaction intermediates, thereby facilitating the entire EOR process. Moreover, a VOx-Ni3N-based electrolyzer, coupling hydrogen evolution reaction (HER) and EOR, attains 50mA cm-2 at a low cell voltage of ≈1.5V. This work thus paves the way for creating dual polarization through interface engineering toward broad catalysis.

Electrosynthesis of adipic acid with high faradaic efficiency within a wide potential window

Electrosynthesis of adipic acid (a precursor for nylon-66) from KA oil (a mixture of cyclohexanone and cyclohexanol) represents a sustainable strategy to replace conventional method that requires harsh conditions. However, its industrial possibility is greatly restricted by the low current density and competitive oxygen evolution reaction. Herein, we modify nickel layered double hydroxide with vanadium to promote current density and maintain high faradaic efficiency (>80%) within a wide potential window (1.5 ~ 1.9 V vs. reversible hydrogen electrode). Experimental and theoretical studies reveal two key roles of V modification, including accelerating catalyst reconstruction and strengthening cyclohexanone adsorption. As a proof-of-the-concept, we construct a membrane electrode assembly, producing adipic acid with high faradaic efficiency (82%) and productivity (1536 μmol cm−2 h−1) at industrially relevant current density (300 mA cm−2), while achieving >50 hours stability. This work demonstrates an efficient catalyst for adipic acid electrosynthesis with high productivity that shows industrial potential.

Spin Manipulation of Co sites in Co9S8/Nb2CTx Mott-Schottky Heterojunction for Boosting the Electrocatalytic Nitrogen Reduction Reaction.

Regulating the adsorption of an intermediate on an electrocatalyst by manipulating the electron spin state of the transition metal is of great significance for promoting the activation of inert nitrogen molecules (N2) during the electrocatalytic nitrogen reduction reaction (eNRR). However, achieving this remains challenging. Herein, a novel 2D/2D Mott-Schottky heterojunction, Co9S8/Nb2CTx-P, is developed as an eNRR catalyst. This is achieved through the in situ growth of cobalt sulfide (Co9S8) nanosheets over a Nb2CTx MXene using a solution plasma modification method. Transformation of the Co spin state from low (t2g 6eg 1) to high (t2g 5eg 2) is achieved by adjusting the interface electronic structure and sulfur vacancy of Co9S8/Nb2CTx-P. The adsorption ability of N2 is optimized through high spin Co(II) with more unpaired electrons, significantly accelerating the *N2→*NNH kinetic process. The Co9S8/Nb2CTx-P exhibits a high NH3 yield of 62.62µg h-1 mgcat. -1 and a Faradaic efficiency (FE) of 30.33% at -0.40V versus the reversible hydrogen electrode (RHE) in 0.1m HCl. Additionally, it achieves an NH3 yield of 41.47µg h-1 mgcat. -1 and FE of 23.19% at -0.60V versus RHE in 0.1m Na2SO4. This work demonstrates a promising strategy for constructing heterojunction electrocatalysts for efficient eNRR.

Pt Nanoparticles Electrochemically Deposited onto Heteroatom-Doped Graphene Supports as Electrocatalysts for ORR in Acid Media

Platinum nanoparticles (PtNPs) are attached to different single heteroatom-doped (N, S, P, and B) and dual heteroatom-doped (N, B and N, P) graphene nanosheets via electrochemical deposition using the chronoamperometric method, which allowed for strong attachment of the PtNPs onto the support surface. The effect of the support material on the electrocatalytic activity of the PtNPs on the oxygen reduction reaction (ORR) in acidic media is examined. The PtNPs supported on boron-doped graphene exhibit the highest specific activity (1.26 mA cm−2), and the PtNPs supported on nitrogen and boron dual heteroatom-doped graphene exhibit the highest mass activity (0.70 A mg−1) at 0.9 V vs reversible hydrogen electrode. The kinetics of the ORR vary significantly depending on the dopants, thus concluding that the heteroatom doping of the graphene support material affects the electrocatalytic activity of PtNPs toward the ORR.

CsPbBr3-based photoanode prepared by single-step Chemical vapor deposition of tunable thickness perovskite films

Cesium Lead Bromide (CsPbBr3) perovskite films have gained significant attention in photoelectrochemistry due to their promising properties. However, their widespread application necessitates scalable processing methods to produce high-quality films. Current techniques often involve post-synthesis steps to achieve desirable crystalline films or surface coverage for optimal performance. This research performed a single-step Chemical Vapor Deposition (CVD) approach to grow high-quality CsPbBr3 films. This methodology offers precise control over film thickness and grain orientation, crucial for optimizing photoelectrochemical response. The procedure simplifies fabrication by bypassing annealing or toxic solvent excess and growing films directly from CsPbBr3 crystals. Film thickness was controlled by adjusting growth time and precursor mass parameters to examine the photoelectrochemical performance across thicknesses ranging from 0.6 µm to 2.5 µm. Optimal results were achieved with dense, compact films 1.5 µm thick, which exhibited oriented grains along the (121) plane. Optical, structural, and morphological analyses confirmed a predominantly pure orthorhombic phase, although slight impurities were noted in thinner films. The 1.5 µm films showed a four-hour stable photocurrent of 6.2 mA/cm2 at 1.23 V versus reversible hydrogen electrode (RHE) under simulated solar conditions, underscoring their potential in advancing perovskite-based electrodes for efficient photoelectrochemical solar fuel generation.

Role of active redox sites and charge transport resistance at reaction potentials in spinel ferrites for improved oxygen evolution reaction

Fe and Ni oxide-based systems are often investigated as electrocatalysts for the oxygen evolution reaction (OER) in water electrolysis and the improvement in OER activity is explained by two main reasons, (i) improving bulk electrical conductivity and (ii) synergic effect between Ni and Fe. Among the two factors, the identification of the dominant factor for OER is very important for catalyst engineering in the right direction. In order to have a better understanding, spinel-structured ZnFe2O4 nanoparticles have been synthesized and its bulk conductivity is studied by progressively varying Ni doping. The conductivity of the synthesised compounds follows the order of ZnFe2O4 > Ni0.3Zn0.7Fe2O4 > Ni0.5Zn0.5Fe2O4 > Ni0.7Zn0.3Fe2O4 > NiFe2O4. The oxygen evolution studies reveal that NiFe2O4 is highly active with an onset potential of 1.57 V versus reversible hydrogen electrode (RHE) and Tafel slope of 102 mV/dec. With the increase in Ni doping, the structure changes from spinel to inverse spinel as confirmed by X-ray diffraction and Raman spectra. Further, the contribution from Ni redox sites in addition to Fe ion sites and FexNi1−xOOH species formation, causes improved OER performance. This study uniquely proves that the OER activity majorly relies on redox/active metal sites, FexNi1−xOOH species and charge transfer resistance at OER potential rather than the bulk electrical conductivity of spinel ferrites. This conclusion is supported by voltammetry and impedance studies of five different spinel ferrites.

N-doped pitch assisted local interface micro-environment tailoring and microcrystalline regulation in carbon nanotube for efficient oxygen reduction reaction

Regulating the atomic micro-environment at active sites and the interfaces between carbon nanoparticles is crucial for enhancing the performance of carbon-based metal-free electrocatalysts. Herein, a novel carbon nanocomposite, nitrogen-doped coal tar pitch composite carbon nanotubes (NPC@CNTs) was proposed, along with the potential synergistic mechanisms at its heterojunction interfaces. The innovative synthesis involves encapsulating carbon nanotubes (CNTs) within coal tar pitch (CTP), followed by nitrogen doping and CO2 activation to form a layered nano-microstructure with hierarchical porosity. This configuration allows for the precise modulation of the atomic environment at the graphitic-N sites within the heterostructure, with the interfacial effects significantly promoting efficient electron transfer and mass transport. The NPC@CNTs exhibit high Eonset(0.991 V verse Reversible Hydrogen Electrode) and Ehalf-wave(0.845 V vs RHE) in alkaline solution. with an OER overpotential of 391 mV at 10 mA cm−2. Furthermore, a Zn–air battery employing NPC@CNTs indicates a peak power density of 91 mW cm−2 with sustained stability over 230 h. Density Functional Theory (DFT) calculations confirmed the heterostructure of graphitic nitrogen-doped CNTs provides a higher density of active sites and more efficient charge transfer at carbon atoms adjacent to nitrogen. The CNTs with functionalized shell-interface has significant potential for bifunctional catalysis, surpassing most heteroatom-doped nanocarbon catalysts and commercial Pt/C (20 %).