Activated carbon/ZnO composites prepared using hydrochars as intermediate and their electrochemical performance in supercapacitor

doi:10.1016/j.matchemphys.2014.07.058

Materials Chemistry and Physics

Volume 148, Issues 1–2, 14 November 2014, Pages 380-386

https://doi.org/10.1016/j.matchemphys.2014.07.058 Get rights and content

Highlights

•
Hydrochars as intermediate to prepare activated carbon/ZnO composites.
•
Activated carbon/ZnO showed excellent electrochemical performance in supercapacitors.
•
Activated carbon with large surface area can be obtained by removing ZnO.

Abstract

We report a new methodology to prepare activated carbon and activated carbons/ZnO composites from walnut shell-derived hydrothermal carbons (hydrochars), which were prepared under hydrothermal condition in presence of ZnCl₂. For this method, activated carbon/ZnO composites were prepared via heat treatment of hydrochars under inert environment and activated carbons were prepared by removing the ZnO in activated carbon/ZnO composites. The chemical structure of walnut shell, hydrochars, activated carbon/ZnO and activated carbon was investigated by Fourier transform infrared spectroscopy, Raman, X-ray powder diffraction, thermogravimetric analysis and N₂ adsorption/desorption measurements. It is found ZnCl₂ plays multiple roles, i.e., helping to remove the oxygen-containing groups during hydrothermal stage, improving the surface area of activated carbon and acting as the precursor of ZnO in heat-treatment stage. The specific surface areas up to 818.9 and 1072.7 m² g⁻¹ have been achieved for activated carbon/ZnO composites and activated carbon, respectively. The activated carbon/ZnO as electrode materials for supercapacitors showed that specific capacitance of up to 117.4 F g⁻¹ at a current density of 0.5 A g⁻¹ in KOH aqueous solution can be achieved and keeps stable in 1000 cycles.

Introduction

Activated carbon has been taken as an ideal supercapacitor electrode material due to its large surface area and high electrical conductivity [1]. In general, the activated carbon was prepared by physical or chemical activation of biomass precursors [2]. For either physical or chemical activation, thermal treatment which consumes a lot of energies is necessary to pyrolyze and activate biomass precursor. It is very interesting to enhance the energy efficiency to reduce the cost in preparing activated carbon. Hydrothermal carbonization (HTC) has been thought as one of very promising techniques to the conversion of biomass in an energy-saving, cheap and sustainable way [3], [4], [5], [6], [7], [8]. HTC was first proposed by Bergius in 1913 as a synthetic way to mimic coal formation under self-generated pressure in closed systems and mild temperatures (i.e., 130–250 °C) for several hours [9]. The obtained carbon-rich solid (also called hydrochar), which forms through hydrolysis, dehydration, decarboxylation, condensation polymerization, and aromatization reactions, possesses a hydrophilic surface containing a high concentration of oxygen functional groups (i.e., hydroxyl/phenol, carbonyl, or carboxyl). HTC presents many advantages with respect to the traditional pyrolysis techniques employed to obtain carbonaceous materials including higher carbon conversion rate, energy saving due to exothermic reaction and environmental benefits owing to no discharge of toxic gas [10].

Hydrochars which are generally micrometer sized particles possessing an sp² hybridized backbone decorated with numerous polar oxygen-containing functionalities can be used in multiple field including water purification, gas storage, catalysis and electronics [11], [12], [13], [14], [15]. The properties of hydrochars are related to the factors such as reaction temperature, reaction time, precursor concentration inside the autoclave and the reaction recipe. It was found that the presence of additives such as metal ion can effectively accelerate HTC of starch, which shortens the reaction time to several hours [5]. Recent research showed that ZnCl₂, a typical activating reagent for carbon material [16], [17], [18], [19], also has the ability to increase the surface area of hydrochars during HTC [20]. Although hydrochars have many special properties such as self-binding ability, they also suffer two major drawbacks when used as electrode material. One drawback is that their conductivity is low due to the presence of high concentration functional groups as well as low degree of carbonization. The other one is that the specific surface area of hydrochars was small in general. Fortunately, the heat treatment can transform the hydrochars in to activated carbon with increased conductivity owing to the removal of the functional groups on the surface of hydrochars as well as improved carbonization degree. For example, Román et al. have reported the activation process of hydrochars obtained from walnut shell have led to the formation of activated carbons with improved surface area and good porosity [2].

Walnut shell as biomass waste is one ideal precursor for hydrochars due to its cheapness, abundance as well as renewability. Studies have indicated that the hydrochars obtained from biomass resources show an incipient porosity which is favorable to transform hydrochars into porous activated carbon [21].

Considering the study on HTC of biomass in presence of metal ion is very limited and the resulting metal oxide have a pseudo capacitance which is favorable for supercapacitor, here we report the preparation and capacitance behavior of activated carbon/ZnO composites prepared via hydrochars, which was obtained from the HTC of walnut shell in presence of ZnCl₂.

One hand, ZnCl₂ has the ability to increase the surface area of hydrochars. On the other hand, under certain environment ZnCl₂ can transform into ZnO [22], which is a promising electrode material for supercapacitor due to large pseudo capacitance, friendly nature as well as cheapness [23], [24]. Furthermore, the combination of high surface area activated carbon with ZnO would result in utilizing both the faradaic capacitance of the metal oxide and the double layer capacitance of the carbon.

Section snippets

Materials

Walnut shells were obtained from local market in Qinhuangdao. All other reagents were of analytical-grade reagents and used without further purification except otherwise stated. All the solution was prepared using de-ionized (DI) water (18 MΩ cm).

Preparation of activated carbon/ZnO

To prepare activated carbon/ZnO, hydrochar was first prepared as intermediate. In a typical synthesis of precursors, 10 g walnut shell was put in 0, 0.25 M and 2 M ZnCl₂ solution. The mixture was transferred into Teflon-lined stainless steel autoclave

Results and discussion

Fig. 1(A) showed XRD pattern of as prepared hydrochars, in which a broad peak at about 22° corresponding to (002) crystal plane of non-graphitic carbon [25]. As shown in curve b and curve c in Fig. 1(A), there is no peaks related to ZnO or Zn(OH)₂ in XRD patterns of HCZ-1 and HCZ-2. However, the peak at about 22° become wider for HCZ-1 and HCZ-2 compared with that of HC, indicating the structural change of hydrochar owing to the addition of ZnCl₂ under hydrothermal condition. After heat

Conclusion

We reported in this study activated carbon and activated carbon/ZnO composites prepared via hydrochar in presence of different amount of ZnCl₂. The added ZnCl₂ in hydrothermal stage play critical roles, i.e., helping to remove the oxygen-containing groups during hydrothermal stage at high concentration, improving the surface area of activated carbon and acting as the precursor of ZnO in heat-treatment stage. The heat-treatment of hydrochars prepared in presence of ZnCl₂ leads to the formation

Acknowledgments

The authors acknowledge the financial support from National Natural Science Foundation of China (Grant No. 51202212) and Natural Science Foundation of Hebei province (Grant No. E2014203033). The authors also thank Dr. Xue-Mei Li in Shanghai Advanced Research Institute (CAS) for helpful discussions.

References (41)

E. Frackowiak et al.
Carbon materials for the electrochemical storage of energy in capacitors
Carbon
(2001)
S. Román et al.
Production of low-cost adsorbents with tunable surface chemistry by conjunction of hydrothermal carbonization and activation processes
Microporous Mesoporous Mater.
(2013)
Q. Wang et al.
Monodispersed hard carbon spherules with uniform nanopores
Carbon
(2001)
W.T. Tsai et al.
A low cost adsorbent from agricultural waste corn cob by zinc chloride activation
Bioresour. Technol.
(1998)
Z. Yue et al.
Preparation of fibrous porous materials by chemical activation: 1. ZnCl₂ activation of polymer-coated fibers
Carbon
(2002)
J.I. Hayashi et al.
Preparation of activated carbon from lignin by chemical activation
Carbon
(2000)
D. Kalpana et al.
A novel high power symmetric ZnO/carbon aerogel composite electrode for electrochemical supercapacitor
Electrochim. Acta
(2006)
T. Wang et al.
Preparation and characterization of activated carbon from wood via microwave-induced ZnCl₂ activation
Carbon
(2009)
M.A. Serageldin et al.
Coal analysis using thermogravimetry
Thermochim. Acta
(1984)
M. Sevilla et al.
The production of carbon materials by hydrothermal carbonization of cellulose
Carbon
(2009)

Q. Wang et al.

Preparation of carbon micro-spheres by hydrothermal treatment of methylcellulose sol

Mater. Lett.

(2005)

Y. Li et al.

KOH modified graphene nanosheets for supercapacitor electrodes

J. Power Sources

(2011)

M. Selvakumar et al.

Nano ZnO-activated carbon composite electrodes for supercapacitors

Phys. B

(2010)

M. Jayalakshmi et al.

Single step solution combustion synthesis of ZnO/carbon composite and its electrochemical characterization for supercapacitor application

Int. J. Electrochem. Sci.

(2008)

A. Ramadoss et al.

Facile preparation and electrochemical characterization of graphene/ZnO nanocomposite for supercapacitor applications

Mater. Chem. Phys.

(2013)

M.-M. Titirici et al.

Chemistry and materials options of sustainable carbon materials made by hydrothermal carbonization

Chem. Soc. Rev.

(2010)

M.M. Titirici et al.

Replication and coating of silica templates by hydrothermal carbonization

Adv. Funct. Mater.

(2007)

X. Cui et al.

Structural effects of iron oxide nanoparticles and iron ions on the hydrothermal carbonization of starch and rice carbohydrates

Small

(2006)

M. Sevilla et al.

Chemical and structural properties of carbonaceous products obtained by hydrothermal carbonization of saccharides

Chem. Eur. J.

(2009)

H. Sun et al.

Nano-Fe0 encapsulated in microcarbon spheres: synthesis, characterization, and environmental applications

ACS Appl. Mater. Interfaces

(2012)

Cited by (64)

A lignin carbon/bismuth oxide electrode material prepared by electrostatic self-assembly with good stability in supercapacitors
2023, Materials Science and Engineering: B
In this paper, lignin carbon/bismuth oxide (LC/Bi₂O₃) composites were successfully synthesized. They were characterized by X-ray powder diffraction, field emission scanning electron microscopy, Fourier transform infrared spectroscopy, etc. and their electrochemical properties were also tested. The results show that the morphology of LC/Bi₂O₃ composites is lignin pellets which are surrounded with Bi₂O₃ nanosheets. The lignin carbon in the composites mainly exists in an amorphous structure, and the presence of lignin carbon increases the specific surface area and pores of metal oxides. The electrochemical performance test shows that at the carbonization temperature of 450 °C, LC/Bi₂O₃ will obtain the highest specific capacitance, and after 1000 cycles of testing, the capacitance retention rate reaches 98.99%, which demonstrates that the composite material has good cycle stability. It is found that the specific capacitance of LC/Bi₂O₃–450 °C is 1.3 times and 1.2 times that of Bi₂O₃–450 °C and LC-450 °C, respectively when compared with the control group. This shows that lignin carbon and metal oxides promote and cooperate in electrochemical testing. Furthermore, the composites exhibited properties of pseudocapacitive capacitors, indicating that redox reactions occurred in electrochemical performance tests.
An overview of forest residues as promising low-cost adsorbents
2022, Gondwana Research
Citation Excerpt :
In recent years, the unwanted solid residue formed during hydrothermal gasification and liquidation has received increasing attention and is referred to as hydrochar (Kambo and Dutta, 2015; T. Wang et al., 2018; S. Xu et al., 2021). Due to its properties, such as its versatility in the preparation of precursors of activated carbon, hydrochar can be used in wastewater pollution remediation (Babeker and Chen, 2021; Ferrentino et al., 2020; Tu et al., 2021), soil remediation applications (Abel et al., 2013; Bargmann et al., 2014; Schimmelpfennig et al., 2014), solid fuels (He et al., 2019, 2013; Lin et al., 2015), and other carbonaceous materials (Arenas Esteban et al., 2020; de Oliveira et al., 2017; Li and Liu, 2014). The acidification of the surface of an adsorbent enhances its acidic behavior.
Anthropogenic activities have severely affected biogeochemical cycles on a global scale, resulting in a drastic increase in environmental problems, intensified by wastewater generation containing high levels of pollutants. As it is known that water is precious yet limited, viable wastewater treatments must be developed. Adsorption is an environmentally friendly option, and it offers the possibility of resolving two problems simultaneously. Besides removing pollutants from water, many adsorbents can be produced using wooden forestry residues. Such materials are generally considered as waste, which leads to their direct disposal. In addition, there are types of wooden forestry waste that have little or no use for humankind, such as fallen leaves or rotten fruits. Therefore, the utilization of wooden forestry residues for preparing low-cost adsorbents is promising. In this review, we briefly approach adsorption advantages to wastewater treatment. Later on, we focus on several types of wooden forestry residues as alternative low-cost adsorbents.
A sustainable generated hydrochar from pomegranate residues for remediation of process water contaminated with Cu(II) ions
2021, Advanced Powder Technology
An eco-friendly, flexible and sustainable valorization of pomegranate residue (PR) was studied by hydrothermal technology. PR was used as a feedstock for producing hydrochar (PRHC) and the effects of treatment temperature (TT; 180, 200, 220 °C) and treatment time (Tt; 6, 12, 24 h) on the elemental composition, yield, higher heating value (HHV) and energy density (D_E) parameters were examined. The most suitable production conditions were recommended as TT of 220 °C and Tt of 12 h with a HHV of 23.23 MJ/kg and D_E of 1.22 GJ/m³. A broad spectral survey including FTIR, SEM/EDX, XPS, XRD, Raman and ¹³C MAS-NMR techniques were performed to define its physicochemical characteristics. PRHC was applied as an adsorbent for removal of Cu(II) ions from water and adsorption kinetics indicated well-suitability of the data to the pseudo second order model while the Langmuir model best described the equilibrium data with a 113.64 mg/g. Thermodynamics evaluation displayed the spontaneous, feasible and endothermic adsorption of Cu(II) ions. In addition, regeneration studies have shown efficiently usage of PRHC for multiple times in wastewater treatment.
Natural coconut liquid derived nanosheets structured carbonaceous material for high-performance supercapacitors
2021, Colloids and Surfaces A: Physicochemical and Engineering Aspects
Bio-derived carbon has been remarkably emerging potential candidates for high performance super-capacitive materials. Herein, we report the spray deposited vertically aligned nanosheets (thickness ~ 46 nm) carbon network on nickel foam electrodes using natural coconut liquid as a precursor for high-performance supercapacitor device application. These binder-free fabricated bio-carbon electrodes have characterized using XRD, FESEM, XPS, Raman, Elemental mapping, and EDS. The carbon was coated on nickel foam at different spray pyrolysis deposition times viz. 14, 18 and 22 min. This carbon deposited nickel foam electrodes were investigated for electrochemical characteristics viz EIS, CV, and GCD using 1 M KOH aqueous solution within 0–0.6 V potential window. The electrode CWC-22 exhibited the specific capacitance of 782.7 Fg⁻¹ for 1 Ag⁻¹ current density. The energy density of 12.29 W h/kg and 1600 W/kg power density were achieved for CWC-22 electrode. The stability of the CWC-22 was studied by performing 3000 GCD cycles with excellent capacitance retention rate of 89.4% recorded at 5 Ag^–1. The device fabrication and demo performance were also studied. This approach has the potential to accomplish cost-effective, green synthesized bio-derived carbon for high-performance electrochemical supercapacitor devices.
Novel structure of bacteria doped ZnO particles: Facile and green synthesis route to prepare hybrid material for supercapacitor electrodes
2021, Journal of Industrial and Engineering Chemistry
Zinc oxide (ZnO) nanostructures/bacteria (Escherichia coli, E. coli) composite material is successfully prepared via carbonization process. Morphological and electrochemical properties of nanostructure were studied as function of concentration of bacteria solution. Morphological properties of the composite material were investigated by scanning electron microscopy (SEM) and Brunauer–Emmett–Teller (BET). The new approach of high-performance electrodes based on carbonization prepared from precursor and reductant of ZnO and bacteria resources. The ZnO nanostructures were reacted with the bacteria to introduce carbon (C) and nitrogen (N) for better electrochemical performance and an increased surface area. The bacteria doped ZnO electrode exhibited significantly enhanced specific capacitance (41 F g⁻¹) at a discharge current density of 0.5 A g⁻¹, and cycling stability of 55% retention after 5000 cycles. Therefore, the bacteria as electrical dopant gave higher specific capacitance and cycle stability to the other metal oxide which could be a potential candidate in commercial applications of supercapacitors.
ZnO@ activated carbon derived from wood sawdust as adsorbent for removal of methyl red and methyl orange from aqueous solutions
2024, Scientific Reports

View all citing articles on Scopus

View full text

Activated carbon/ZnO composites prepared using hydrochars as intermediate and their electrochemical performance in supercapacitor

Highlights

Abstract

Introduction

Section snippets

Materials

Preparation of activated carbon/ZnO

Results and discussion

Conclusion

Acknowledgments

Carbon

Microporous Mesoporous Mater.

Carbon

Bioresour. Technol.

Carbon

Carbon

Electrochim. Acta

Carbon

Thermochim. Acta

Carbon

Mater. Lett.

J. Power Sources

Phys. B

Int. J. Electrochem. Sci.

Mater. Chem. Phys.

Chemistry and materials options of sustainable carbon materials made by hydrothermal carbonization

Chem. Soc. Rev.

Replication and coating of silica templates by hydrothermal carbonization

Adv. Funct. Mater.

Structural effects of iron oxide nanoparticles and iron ions on the hydrothermal carbonization of starch and rice carbohydrates

Small

Chemical and structural properties of carbonaceous products obtained by hydrothermal carbonization of saccharides

Chem. Eur. J.

Nano-Fe0 encapsulated in microcarbon spheres: synthesis, characterization, and environmental applications

ACS Appl. Mater. Interfaces