Hydrogen production from sodium borohydride originated compounds: Fabrication of electrospun nano-crystalline Co3O4 catalyst and its activity

Electrospun nanofibers are prepared through electrospinning followed by post-treatment and preferred to use in catalytic applications. The electrospinning provides advantages for active catalysts design based on activity profiles and features of catalyst. In the present study, we fabricated nano-crystalline cobalt oxide (Co₃O₄) catalyst by electrospinning technique followed by thermal conditioning. Polyacrylonitrile (PAN) based Co as-spun mats (Co/NMs) with homogeneous diameter were prepared by electrospinnig process under several conditions as applied voltage (15–25 kV), working distance (5–7.5 cm) with the feed rate of 1 ml min⁻¹. The calcination process as a post-treatment was applied at different temperatures (232 °C, 289 °C and 450 °C) to obtain electrospun nano-crystalline Co₃O₄ catalyst. Co/NMs catalysts were characterized by XRD, SEM, TEM, XPS, FT-IR, TG/DTG, and ICP-MS techniques. The parametrically study was performed for evaluating the hydrogen production activity of catalyst from sodium borohydride (NaBH₄, SBH) and its originated compounds as ammonia borane (NH₃BH₃, AB) and methyl-amine borane (CH₃NH₂BH₃, MeAB). The relation between the internal-external properties and catalytic activities of catalysts for hydrogen production was investigated. The beadless Co/NMs-1 catalyst with homogeneous diameter was obtained under electrospinnig process conditions at 15 kV applied voltage and 7.5 cm working distance. All catalysts showed activity for hydrogen production, also the significant effect of post treatment process was observed on the catalytic activity as given order: Co/NMs-1₄₅₀ > Co/NMs-1₂₈₉ > Co/NMs-1 > Co/NMs-1₂₃₂. Furthermore, mesoporous Co₃O₄ cubic crystals (26 nm) in fibrous architecture was prepared by 450 °C-post-treatment. Hydrogen production rates were recorded at 60 °C as 2.08, 2.20, and 6.39 l H₂.g_cat⁻¹min⁻¹ for NaBH₄, CH₃NH₂BH₃, and NH₃BH₃, respectively.     

Self-optimized and renewable Ni–Co alloy@Co–Co2C catalyst for higher alcohols synthesis from syngas

Higher alcohols synthesis (HAS) from syngas (CO/H₂) has attracted widespread attention, while the low selectivity and poor stability of the catalysts mainly stumbled its industrial application. In the work, Ni–Co alloy nanoparticles (NPs) derived from Co_1-xNi_xAl₂O₄ loaded on the SiO₂ with large specific surface area were prepared; and during reaction, the highly dispersed Ni–Co alloys were self-optimized to Ni–Co alloy@Co–Co₂C. Importantly, Ni–Co alloy@Co–Co₂C can be regenerated through oxidation - reduction - self-optimization process. Characteristic results indicated that the structural liberalization during the reaction process inhibited the loss of Ni, regulated and balanced the dual active sites of the catalyst and the Ni–Co alloys were regenerated after the re-oxidation and re-reduction process. The optimized catalyst exhibited excellent catalytic performance, including a high total selectivity to alcohols of 39.3% and an excellent catalytic stability at 250 °C, 3.5 MPa (H₂/CO = 2) and a space velocity of 6000 mL (g_cat h)^?1. In addition, the Ni–Co alloy@Co–Co₂C catalyst after stability test could recover its original catalytic performance after re-oxidation and re-reduction. The renewable characteristics and superior catalytic performance of Ni–Co alloy@Co–Co₂C made the catalyst to be one of the potential industrial catalysts for HAS.     

Protection and confinement effect of carbon on Co/CoxOy nano-catalyst for efficient NaBH4 hydrolysis

The hydrolysis of sodium borohydride (NaBH₄) over catalysts is a promising method to produce hydrogen. Although Co-based catalysts exhibit high activity for NaBH₄ hydrolysis, they are still far from satisfying practical applications, especially their poor durability in alkaline media. Herein, a carbon shell structure was designed and synthesized to improve the stability of the mixture of Co⁰ and Co_xO_y nanofilms (Co/Co_xO_y@C) during NaBH₄ hydrolysis via a facile polymerization-pyrolysis strategy with Co/Co_xO_y nanofilms as the precursor. As a result, the Co/Co_xO_y@C catalyst can achieve a remarkable H₂ generation rate of 4348.6 mL min^?1 g_Co^?1 with a low activation energy of 43.6 kJ mol^?1, which is superior to most previously reported catalysts. Moreover, the catalyst shows high stability with an H₂ generation-specific rate of 79% after five cycles. The excellent performance of carbon substrate can well prevent the agglomeration of Co-based nanoparticle and improve the corrosion resistance of the active Co to BO₂^? and OH^?. This work would widen the road for the preparation of nanoconfined catalysts, which has prospective application potentials for H₂ production from NaBH₄ hydrolysis.     

Porous Co3O4 decorated nitrogen-doped graphene electrocatalysts for efficient bioelectricity generation in MFCs

High-performance, low-cost, and robust oxygen reduction reaction (ORR) catalysts have played a very crucial role in the development of microbial fuel cells (MFCs). Herein, A novel in-situ Co₃O₄ nanoparticles (NPs) modified nitrogen-doped graphene with three-dimensional porous structure (3D GN-Co₃O₄) has been successfully synthesized and employed as an efficient ORR catalyst in MFCs. Benefiting from 3D porous architecture feature, highly intrinsic conductivity and synergistic effect between nitrogen-doped graphene and Co₃O₄ NPs, the 3D GN-Co₃O₄ as a cathode catalyst in alkaline condition realizes significantly enhanced electrochemical performance and outstanding cycling stability. Furthermore, the self-assembly of MFCs based on the 3D GN-Co₃O₄ cathode offers a high power density of 578 ± 10 mW m^?2, which is even comparable to the commercial Pt/C.     

ZIF-L-Co@carbon fiber paper composite derived Co/Co3O4@C electrocatalyst for ORR in alkali/acidic media and overall seawater splitting

Green and clean energy technologies, including fuel cells, metal-air batteries, water splitting et al., are becoming more significant for our lives. Oxygen reduction reaction (ORR), hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) are key reaction processes for fuel cells, metal-air batteries and water splitting. Therefore, it is highly desirable to design a multifunctional catalyst, which owns catalytic performance under a widely applied range. Herein, we demonstrate a novel multifunctional catalyst (Co/Co₃O₄@C) by carbonizing a composite material constructed of zeolite imidazolate framework and carbon fiber paper (ZIF-L-Co@CP). It is a carbon-based material containing metallic Co and Co₃O₄ as a low-cost and effective catalyst toward the ORR and overall water splitting. For ORR, the Co/Co₃O₄@C catalyst shows high half-wave potential in both alkaline and acidic media, 0.823 V for 0.1 M KOH and 0.672 V for 0.1 M HClO₄. More importantly, it exhibits good catalytic activities of hydrogen and oxygen evolutions to perform overall splitting in actual seawater.     

Co2P nanoparticles supported on cobalt-embedded N-doped carbon materials as a bifunctional electrocatalyst for rechargeable Zn-air batteries

Reversible oxygen electrodes with high efficiencies for the oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) are of great significance for a variety of energy conversion devices, such as fuel cells and metal-air batteries. Herein, Co₂P nanoparticles supported on cobalt-embedded N-doped carbon materials (Co₂P/Co–N–C) have been prepared by pyrolysis of cobalt zeolitic imidazolate framework and phosphating post treatment. The optimal Co₂P/Co–N–C composite shows excellent bifunctional electrocatalytic activities for both OER (the potential of 1.65 V at 10 mA cm^?2) and ORR (half-wave potential of 0.82 V). As a practical demonstration, Co₂P/Co–N–C catalyst is used as an air electrode in liquid Zn-air battery, which displays a large open-circuit voltage of 1.50 V, a high peak-power density of 158 mW cm^?2 and excellent reversibility of over 205 h at 5 mA cm^?2. Moreover, the flexible Zn-air battery with Co₂P/Co–N–C exhibits a high open-circuit voltage of 1.46 V and the good flexibility with different angles. This work provides inspiration to explore new strategies for electrochemical energy conversion and storage.     

Well-dispersed Co–Co3O4 hybrid nanoparticles on N-doped carbon nanosheets as a bifunctional electrocatalyst for oxygen evolution and reduction reactions

Bifunctional catalysts are vital for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) in metal-air batteries. In this work, Co–Co₃O₄/N-doped carbon nanosheets (NCNs) were developed as highly efficient bifunctional oxygen catalysts via the pyrolysis of a hybrid ZIF-67/CNs precursor. It is found that the introduced CNs play important roles. On one hand, the introduced CNs can tune the surface contents of Co, N and/or O species that are closely correlated with OER and ORR activity. On the other hand, they also facilitate to achieve high specific surface areas for the catalysts. In addition, the introduced CNs helps the formed Co–Co₃O₄ hybrid nanoparticles with uniform and small sizes to be well-distributed on the NCNs substrates. Despite such important roles, it should be noted that a moderate content of the introduced CNs is required to achieve optimal oxygen catalytic activity. As a result, the optimized ZIF-67/CNs(1)-600 exhibits a low value of η₁₀ (~350 mV) for OER and a high value of E_1/2 (~0.85 V) for ORR. Its overall bifunctional activity (ΔE) is as low as ~0.73 V, which is comparable to the recent reported Co-based catalysts.     

Heterostructured Co3O4/VO2 nanosheet array catalysts on carbon cloth for hydrogen evolution reaction

Developing highly efficient, low-cost, and robust water splitting hydrogen production catalysts is critical for hydrogen energy applications. This study presents the synthesis of Co₃O₄/VO₂ heterogeneous nanosheet structures on carbon cloth (Co₃O₄/VO₂/CC). The obtained Co₃O₄/VO₂/CC hybrid catalyst has a low overpotential of 108 mV at a current density of 10 mA cm^?2, a Tafel slope of 98 mV dec^?1, and high stability in 1.0 M KOH for 10 h. The experimental results and density functional theory (DFT) calculations results also show that Co₃O₄ coupled with VO₂ in Co₃O₄/VO₂/CC can optimize hydrogen adsorption energy and facilitate electron transport, thereby accelerating the catalytic kinetics for hydrogen evolution reaction (HER). This work also provided an alternative method to design and construct non-noble metal oxide-based catalysts for alkaline hydrogen production.     

Co−O−P composite nanocatalysts for hydrogen generation from the hydrolysis of alkaline sodium borohydride solution

In recent years, catalytic hydrolysis of sodium borohydride is considered to be a promising approach for hydrogen generation towards fuel cell devices, and highly efficient and noble-metal-free catalysts have attracted increasing attention. In our present work, Co₃O₄ nanocubes are synthesized by solvothermal method, and then vapor-phase phosphorization treatment is carried out for the preparation of novel Co−O−P composite nanocatalysts composed of multiple active centers including Co, CoO, and Co₂P. For catalyst characterization, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD) and X-ray photoelectric spectroscopy (XPS) are conducted. Optimal conditions for catalyst preparation and application were investigated in detail. At room temperature (25 °C), maximum hydrogen generation rate (HGR) is measured to be 4.85 L min⁻¹ g⁻¹ using a 4 wt% NaBH₄ − 8 wt% NaOH solution, which is much higher than that of conventional catalysts with single component reported in literature. It is found that HGR remarkably increases with the increasing of reaction temperature, and apparent activation energy for catalytic hydrolysis of NaBH₄ is calculated to be 63 kJ mol⁻¹. After reusing for five times, the Co−O−P composite nanocatalysts still retains 78% of the initial activity.     

Highly efficient Co/NC catalyst derived from ZIF-67 for hydrogen generation through ammonia decomposition

Small-size cobalt nanoparticles (NPs) distributed on nitrogen doped carbon support (Co/NC-X) were prepared by pyrolysis of ZIF-67 at various temperatures (X = 500, 600,700 and 800 °C) in nitrogen atmosphere and utilized as catalysts for hydrogen production through ammonia decomposition. Characterizations of the catalysts including XRD, HRTEM, XPS, H₂-TPR, CO₂-TPD, etc., were conducted for structure analysis. The N–C plate obtained from pyrolysis was coated with Co NPs to hinder its aggregation, which made the Co NPs dispersed evenly and increased their dispersion. The calcination temperature and the strong base of the support can adjust the strength of Co–N bond. The activity of the Co/NC-X catalysts is attributed to the high content of Co⁰ and the moderate Co–N bond strength. The ammonia decomposition activity of Co/NC-X catalysts in this paper is higher than many reported Co-based catalysts. Co/NC-600 catalyst demonstrates an ammonia conversion of 80% at 500 °C with a space velocity of 30,000 ml g_cat^?1 h^?1, corresponding to a hydrogen production rate of 26.8 mmol H₂ g_cat^?1 min^?1. The work provides insight for the development of highly active cobalt-based catalysts for hydrogen production through ammonia decomposition.     

Enhanced electrochemical activity of Co3O4/Co9S8 heterostructure catalyst for water splitting

The dearth of efficient, robust, and economical electrocatalysts for water oxidation is dubiously the key obstacle for renewable energy devices, so synthesis of efficient, and cost-effective metal-based water oxidation catalysts is vital. Herein, Co₃O₄, Co₉S₈ catalysts and their heterostructure Co₃O₄/Co₉S₈ were synthesized and evaluated as water oxidation electrocatalysts. The characterization of Co₃O₄, Co₉S₈, and Co₃O₄/Co₉S₈ electrocatalysts was performed using Fourier transform infrared spectroscopy, scanning electron microscopy and X-ray diffraction techniques. The heterostructure Co₃O₄/Co₉S₈ (1.46 V) exhibited water oxidation electrocatalysis at extremely low onset potential compared to Co₃O₄ (1.58 V), and Co₉S₈ (1.48 V) catalysts. A 281 mV overpotential required to attain a current density of 50 mA cm^?2 in alkaline solution (1 M KOH), outperforming most of Co-based benchmark electrocatalysts. Further, the Co₃O₄/Co₉S₈ heterojunction demonstrated catalytic activity with small Tafel slope of 37 mV dec^?1. The finding of electrochemical studies involving controlled potential electrolysis and long-term stability are projected to steer the future advancement in constructing efficient, economical, stable, and earth-abundant metal-based water oxidation catalysts.     

Steam reforming of toluene as model compound of biomass tar over Ni–Co/La2O3 nano-catalysts: Synergy of Ni and Co

A series of LaNi_1-xCo_xO₃ (x = 0, 0.2, 0.5, 0.8 and 1) perovskite catalysts were prepared successfully and applied for toluene steam reforming as a model tar molecule. The Ni–Co alloy formation in reduced LaNi_1-xCo_xO₃ was confirmed by TPR, XRD and XPS. The strong interaction in LaNi_0.8Co_0.2O₃ between Ni and Co produced highly dispersed and smaller metal (8–9 nm), higher reducibility and larger amounts of active sites as well as more abundant oxygen defects and higher surface/lattice oxygen mobility, confirmed by XRD, TEM, TPR, XPS and O₂-TPD. Also, a higher electron density prevented Ni from oxidation and sintering; a more oxidized Co (Co³⁺) facilitated the dissociation of water and activation of CO₂, thus removing the coke. At 600 °C, S/C = 3.4 and WHSV = 16.56 ml h⁻¹ g_cat⁻¹, an equilibrium conversion was achieved initially and over 80% conversion after 24 h were obtained for LaNi_0.8Co_0.2O₃ with a high H₂ yield (81.8% at maximum) and 8.0 of H₂/CO ratio. The graphitic/filamentous coke formation was alleviated and no metal sintering was presented after the reaction.     

Co–Co3O4 nanostructure with nitrogen-doped carbon as bifunctional catalyst for oxygen electrocatalysis

In view of the development of advanced bi-functional oxygen electrodes for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), herein, we report the synthesis of Co–Co₃O₄ nanostructure encased in N-doped carbon (Co–Co₃O₄/NC) by carbothermal reduction followed by controlled oxidative treatment. The formation of a protective-active oxide layer on the metallic-Co not only facilitated the effective charge separation and transport but also displayed improved stability of Co–Co₃O₄/NC in an alkaline operating condition. The Co–Co₃O₄/NC catalyst afforded 0.810 V overvoltage between ORR and OER in 0.1 M KOH solution, consequently, this lower reversible overvoltage would result in energy saving of around 0.246 V if Co–Co₃O₄/NC is used as an oxygen electrode instead of commercially available 40 wt % Pt/C. Furthermore, in comparison with the use of Pt/C + IrO₂ as an ORR and OER catalyst, respectively the single bi-functional electrocatalyst i.e., Co–Co₃O₄/NC would result in energy saving of around 0.13 V.     

Hollow bimetal ZIFs derived Cu/Co/N co-coordinated ORR electrocatalyst for microbial fuel cells

A simple method for synthesizing highly active electrocatalyst with bimetal Cu/Co and N co-doped porous carbon structures framework is reported in this study. The addition of Cu and Co elements improve the chemical and physical properties of the electrocatalyst, including abundant valid active sites, large specific surface area and good conductivity, which significantly boost electrocatalytic performances in oxygen reduction reaction (ORR). The onset and half-wave potentials of catalyst (Cu/Co/N–C#2) are 0.25 and 0.14 V (vs Ag/AgCl), respectively, which are positive than those of the 20% Pt/C catalysts. Moreover, the maximum output voltage and power density of the Cu/Co/N–C#2 catalyst-based air-cathode microbial fuel cells (MFCs) are enhanced to 677 mV and 1008 mW m⁻², respectively, which are 1.25 and 1.31 times higher than those of the 20% Pt/C catalyst-based MFCs. This strategy using Cu-doped ZIF-67 as precursor to prepare bimetal- and nitrogen-codoped hollow carbon structures is a feasible method to boost ORR catalytic performance.     

Bimetallic zeolitic imidazole framework derived Co@NC materials as oxygen reduction reaction catalysts application for microbial fuel cells

Microbial fuel cells (MFCs), a promising future energy conversion technology, play a significant role in the area of sustainable and renewable energy. In air-cathode MFCs, the catalytic activity for oxygen reduction reaction (ORR) of cathode electrocatalyst is the key factor to the performance of MFCs. Development of efficient and economical ORR electrocatalysts is an important step for the wide application of MFCs. Herein, Co wrapped carbon nanotubes (CNTs) N-doped nanoporous carbon materials (Co@NC-Co_xZn_y) are constructed via a facile zinc-assisted growth pyrolytic approach of bimetallic zeolitic imidazole frameworks (BMZIFs)-derived strategy. They are directly prepared via carbonization of the precursor Co_xZn_y-BMZIFs. During the pyrolysis process, the evaporation of zinc plays critical role in the in-situ growth of CNTs. For instance, the optimal catalyst, Co@NC-Co₁Zn₃, exhibits excellent ORR performance activity and stability with on-set potential (E_on-set) of 0.830 V (vs. RHE) and diffusion-limited current density (j_L) of 6.706 mA cm^?2, which is superior to the benchmark catalyst of commercial 20 wt% Pt/C. Additionally, Co@NC-Co₁Zn₃ displays four-electron pathway, long-term stability and better resistance to methanol tolerance. The MFC with Co@NC-Co₁Zn₃ cathode shows a maximum power density of 1039 mW m^?2, and outperforms the MFC with commercial 20 wt% Pt/C catalyst (678 mW m^?2). This work paved the way for exploring cost-effective, superior performance non-precious metal-based catalysts for air-cathode MFCs.     

Catalytic behavior of Pr1-xBa1+xCo2O6-δ in alkaline medium

In this work, a series of double perovskite oxide materials Pr_1-xBa_1+xCo₂O_6-δ (x = 0.05, 0.10, 0.15, and 0.20) was synthesized using the solid-state route method. Their catalytic activity and stability in 1 M KOH alkaline medium were investigated. The phase formation and structure of the prepared oxides were determined by Powder X-ray diffraction. The morphology of prepared catalysts was confirmed by SEM analysis. The catalytic performance of the prepared catalyst in alkaline solution was investigated using electrochemical measurements for both oxygen evolution reaction (OER) and oxygen reduction reactions (ORR). This series of double perovskite oxide materials exhibit catalytic activity for both OER and ORR. Pr_0.90Ba_1.10Co₂O_6-δ shows wonderful OER activity among all the catalysts with a specific capacitance of 598.40 F/g and double-layer capacitance of 38.94 mF/cm². Power low gives a hint of oxide-ion intercalation pseudocapacitance in the Pr_0.90Ba_1·10Co₂O_6-δ. On the other hand, Pr_0.95Ba_1·10Co₂O_6-δ exhibits potential behavior for ORR. Overall, our findings highlight the combined effects of incorporating Ba into double perovskite PrBaCo₂O_6-δ in its behavior for OER and ORR.     

Modulating Fischer-Tropsch synthesis performance on the Co3O4@SixAly catalysts by tuning metal-support interaction and acidity

ZIF-67 derived catalysts for Fischer-Tropsch synthesis have attracted much attention in recent years, while there is still a potential to improve their activity and selectivity. In this work, we prepared Si/Al co-immobilized Co₃O₄@Si_xAl_y catalysts by in-situ doping tetraethylorthosilicate and aluminum nitrate during the synthesis of ZIF-67. The effects of different Si/Al ratios on the metal-support interaction, acidity and FTS performance were explored. Results indicated that the Co₃O₄@Si₀Al₄ catalyst exhibited the best FTS performance with the CO conversion as high as 79.9% and CTY (cobalt time yield) value of 19.5 × 10^?5 mol_CO·g_Co^?1·s^?1, which was ascribed to the moderate metal-support interaction and the most active Co sites. Meanwhile, the Co₃O₄@Si₃Al₁ and Co₃O₄@Si₂Al₂ catalysts exhibited higher iso-paraffin and olefin selectivity due to more acidic sites.     

One-step hydrothermal synthesized 3D P–MoO3/FeCo LDH heterostructure electrocatalysts on Ni foam for high-efficiency oxygen evolution electrocatalysis

Low-cost yet high-efficiency oxygen evolution reaction (OER) catalysts have attracted ardent attention to speed up the development of water electrolysis. Recent researches have shown that layered double hydroxides (LDH) are promising candidates towards OER, but further improvement is still highly demanded for its large-scale practical application in water splitting. Herein, we report a 3D P-doped MoO₃/FeCo LDH/NF (P–MoO₃/FeCo LDH/NF) ultrathin nanosheet heterostructure electrocatalyst with an extremely low overpotentials of 225 mV for delivering a current density of 10 mA cm^?2 for OER and a great durability for at least 80 h by a simple one-step hydrothermal method. Extraordinarily, the P–MoO₃/FeCo LDH catalyst achieves a high current density of 300 mA cm^?2 and even 350 mA cm^?2 at an extremely low overpotential of 297 mV and 302 mV, respectively, which is crucial for the water electrolysis industry. The remarkable performance may be attributed to that the heterostructure between P–MoO₃ and FeCo LDH not only optimizes electronic structure, thus inducing electron transfer from P–MoO₃ to FeCo LDH and then realizing fast electron transfer rates, but also produces more catalytic active sites. Moreover, the synergetic effect between MoO₃ and FeCo LDH also plays an essential role for enhancing the catalytic performances. This work explores the effect of phosphomolybdic acid on the structure, composition and performances of FeCo LDH catalysts, and also provides a simple and cost-effective way to prepare high-efficiency and low-cost layered double hydroxide electrocatalysts for OER.     

Effects of binary Co–Mn oxides promoters on low-temperature catalytic performance of Pd/Al2O3 for methane combustion

Aiming at fabricating high-activity and stable methane combustion catalysts in the dry/wet conditions, Co–Mn binary oxides were employed as promoters to Pd/Al₂O₃ system herein. The introduction of appropriate amount of manganese made Mn³⁺ maximally enter into the Co₃O₄ spinel structure, conducive to the conversion of Co³⁺ to Co²⁺ by Mn³⁺ and then the enhancement of lattice distortion. Therefore, abundant oxygen vacancies were produced, which enhanced the surface-concentrations of active Pd²⁺ and O_ads species, together with the exchange of oxygen species. The resulting catalyst with a molar Mn/Co ratio of 0.20 performed superior low-temperature activity and durability. Moreover, the synergy of Mn and Co could accelerate the removal process of accumulated OH/H₂O from the active sites, thereby promoting the regeneration of PdO and oxygen vacancies. This endowed the tailored catalyst with remarkable moisture-tolerance and hydrothermal stability, and inspiring enhanced activity (T₉₀ = 350 °C) after removing water vapor.     

Bimetallic ZnCo zeolitic imidazolate framework/polypyrrole-polyaniline derived Co/N-doped carbon for oxygen reduction reaction

Non-noble-metal based materials with high activity for oxygen reduction reaction (ORR) are urgently required to substitute Pt-based materials. Herein, metallic Co/N-doped carbon electrocatalysts were synthesized via a facile pyrolysis method of bimetal ZIF(ZnCo)/polypyrrole-polyaniline (ppy-pani) precursors. The evaporation of Zn and the introduced ppy-pani can lead to the porous structure and effectively hinder the aggregation of Co species, which results in the small nanoparticles uniformly distributed on carbon matrices. A high ECSA and a high content of Co species are obtained after the introduction of ppy-pani, thus resulting in the abundant Co²⁺ species to enhance ORR. Therefore, the optimized ZIF/ppy-pani-750 exhibits a high E_1/2 (~0.86 V) and a low Tafel slope (~43.6 mV dec⁻¹).