Duckweed derived nitrogen self-doped porous carbon materials as cost-effective electrocatalysts for oxygen reduction reaction in microbial fuel cells

https://doi.org/10.1016/j.ijhydene.2020.03.177Get rights and content

Highlights

  • NPC was successfully prepared by direct pyrosis and activation of duckweed.

  • Oxygen was efficiently reduced to water through a four-electron pathway on NPC.

  • NPC exhibited comparable performance and better stability to Pt/C catalyst in MFC.

Abstract

Cost-effective metal-free electrocatalysts for oxygen reduction reaction were incredible significance of improvement about microbial fuel cells. In this research, a novel nitrogen self-doped porous carbon material is effectively inferred with KOH activation from a natural and renewable biomass, duckweed. Self-doped nitrogen in carbon matrix of nitrogen-doped porous carbon at 800 °C provides abundant active sites for oxygen reduction and improves the oxygen reduction kinetics significantly. Moreover, the porous structure of nitrogen-doped porous carbon at 800 °C encourages the transition of electrolyte and oxygen molecules throughout the oxygen reduction reaction. Oxygen on the three-phase boundary is reduced to water according to a four-electron pathway on nitrogen-doped porous carbon electrocatalyst. The single-chamber microbial fuel cell with nitrogen-doped porous carbon as electrocatalyst achieves comparable power density (625.9 mW m−2) and better stability compared to the commercial Pt/C electrocatalyst. This simple and low-cost approach provides a straightforward strategy to prepare excellent nitrogen-doped electrocatalyst derived from natural and renewable biomass directly as a promising alternate to precious platinum-based catalysts in microbial fuel cells.

Introduction

Microbial fuel cells (MFCs), a promising and sustainable technology, are employed for wastewater treatment and electronic generation, simultaneously [[1], [2], [3]]. Practical applications have been primarily limited by finite cathode performance and high cost of electrode materials. Particularly, oxygen reduction reaction (ORR) in pH-neutral condition has sluggish reaction kinetics which would cause poor cathode performance and further hinder the commercialization of MFCs [[4], [5], [6]]. Pt-based noble metal materials are most widely used electrocatalysts for the ORR. Nevertheless, the high-cost and scarcity of noble electrocatalysts and weak stability of Pt in long-term operation largely impede the practical application of MFCs. Therefore, the development of cheap, highly active and rich reserves electrocatalysts is necessary for the sustainable development and application of MFCs [7,8].

In recent years, enormous efforts are dedicated to investigating low-cost electrocatalysts for ORR to alternate the precious Pt electrocatalyst, such as based electrocatalyst materials based on reducing noble metal content [9,10], transition metal compounds [11,12] and carbon-based materials [13]. As mentioned in literature, noble metal and transition metal-based materials show excellent activity on ORR in MFCs, however, their costs were still high for the practice application of MFCs. In addition, metal based electrocatalysts suffer anti-toxicity in neutral media and has relatively poor stability compared to carbonaceous materials [14]. Thus, carbonaceous materials, especially the biomass derived carbon materials, should be a promising alternate to noble metal catalysts in microbial fuel cells, which might be owing to the properties of low-cost, comparable catalytic activity, sustainability and high stability [[15], [16], [17]]. The graphene and carbon nanotubes have been widely as ORR catalysts owing to the unique structure and high conductivity [[17], [18], [19]]. Even though, the activity of ORR in microbial fuel cells needs to be further improved for practical applications.

An effective strategy to enhance ORR activity is the doping of heteroatoms (such as N, B, P and S) [20,21], which could increase the active sites and enhance the electron transfer. Among various doped-heteroatoms, carbon materials doped with nitrogen are prospective alternative of noble metal electrocatalysts, owing to that nitrogen-doped carbon matrix provides more actual active sites on N–C structure for ORR and promotes electron transfer between carbon electronic bands of carbon and antibonding orbitals of oxygen [22,23]. Compared to commercial Pt/C electrocatalysts, mesoporous graphene electrocatalyst doped with sulfur and nitrogen showed higher current density and superior durability for oxygen reduction reaction [24]. The novel carbon materials, such as graphene and carbon nanotube, were still too expensive for practice application. Recently, carbon materials derived from earth-abundant and renewable biomass had attracted great research interests in the application of electrocatalysts for ORR and microbial fuel cells [25,26]. Usually, nitrogen doping is achieved by introducing ammonia gas or adding other nitrogen-containing species into the precursor, which increases the cost and complexity of the preparation. Thus, a novel strategy for nitrogen doping is using nitrogenous substances as precursors to prepare nitrogen self-doped materials by direct pyrolysis.

Duckweed, Lemna minor, which is a common water floating plant and growing in paddy fields, ponds or other hydrostatic water, is rich in crude proteins. In some case, Duckweed grows in eutrophic rivers or ponds frantically, causing fish and shrimp to die due to hypoxia. Thus, duckweed grows madly in eutrophic water body and generally be considered as organic waste. On the other hand, the rich biological protein of duckweed might be benefit for the formation of N-doped active centers to enhance the ORR activity in pH-neutral condition [27,28]. Therefore, new strategies to construct carbon materials with in-situ doping nitrogen by direct carbonization of biomass for cost-efficient improve cathode performance and higher operation stability are urgently needed for the application of MFCs.

Herein, a novel nitrogen-doped ORR electrocatalysts was directly derived from a renewable biomass, common duckweed, with KOH as activator to enhance power generation in MFCs. The as-prepared electrocatalysts were investigated through systematical physical and chemical characterization. The activity and mechanism towards oxygen reduction reaction of the duckweed derived electrocatalysts was evaluated in neutral electrolyte. Meanwhile, the maximum power density and stability of duckweed derived electrocatalysts in air-cathode MFCs were also evaluated and compared with commercial Pt/C. On basis of porous structure and nitrogen-doping effect, the MFC with as-prepared electrocatalysts exhibited comparable ORR activity and better stability than that with commercial Pt/C electrocatalyst.

Section snippets

Preparation of N-doped porous carbon

The N-doped porous carbon was prepared by a two-stage carbonization process. Briefly, duckweed was collected from a campus pool and washed with deionized water for several times. The collected duckweed was dried in an oven at 100 °C for at least 24 h. The dried duckweed was ground into small powder and used as precursors for the direct carbonization. And then, the precursors were pre-carbonized under N2 flow (60 mL min−1) at 300 °C for 2 h to further remove internal free-water and bound-water.

Characterization of duckweed-derived porous carbon

Scanning electron microscopy was carried out to observe the porous structures of the obtained carbon materials. Fig. 1 displays the micromorphology and elements distribution of the porous carbon sample obtained at 800 °C. As shown in Fig. 1a, the obtained NPC-800 had a bulk and less porosity surface, while the NPC-800-K activated by KOH exhibited a rather rough and loose surface. It can be seen that the carbon material by KOH activation exhibited a porous and spongy structure, indicating that

Conclusions

A nitrogen self-doped porous carbon material was successfully prepared by direct pyrolysis carbonization of readily available natural and renewable biomass, duckweed. The as-prepared NPC was used as electrocatalyst for promoting oxygen reduction reaction in MFCs. The NPC-800-K exhibited apparent electrocatalytic activity toward for ORR in four-electron pathway with good electrochemical stability. The large surface area, abundant porous structure and self-doping of nitrogen elements in carbon

Acknowledgements

This work was supported by the National Natural Science Foundation of China (No. 51708374) and the Foundation of Education Department of Sichuan Provincial (No. 18ZA0399).

References (47)

  • W. Yang et al.

    Bamboo charcoal as a cost-effective catalyst for an air-cathode of microbial fuel cells

    Electrochim Acta

    (2017)
  • X.-B. Gong et al.

    Silver–tungsten carbide nanohybrid for efficient electrocatalysis of oxygen reduction reaction in microbial fuel cell

    J Power Sources

    (2013)
  • L. Zhou et al.

    Self-constructed carbon nanoparticles-coated porous biocarbon from plant moss as advanced oxygen reduction catalysts

    Appl Catal B Environ

    (2016)
  • L.-Y. Zhang et al.

    Nitrogen-doped microporous carbon: an efficient oxygen reduction catalyst for Zn-air batteries

    J Power Sources

    (2017)
  • L. Zhou et al.

    Naturally derived carbon nanofibers as sustainable electrocatalysts for microbial energy harvesting: a new application of spider silk

    Appl Catal B Environ

    (2016)
  • E. Antolini

    Nitrogen-doped carbons by sustainable N-and C-containing natural resources as nonprecious catalysts and catalyst supports for low temperature fuel cells

    Renew Sustain Energy Rev

    (2016)
  • X. Wang et al.

    Tubular nitrogen-doped carbon materials derived from green foxtail as a metal-free electrocatalyst in microbial fuel cells for efficient electron generation

    Bioelectrochemistry

    (2019)
  • Y. Yuan et al.

    Sewage sludge biochar as an efficient catalyst for oxygen reduction reaction in an microbial fuel cell

    Bioresour Technol

    (2013)
  • Y. Lu et al.

    Biomass-derived heteroatoms-doped mesoporous carbon for efficient oxygen reduction in microbial fuel cells

    Biosens Bioelectron

    (2017)
  • S. Gao et al.

    Honeysuckles-derived porous nitrogen, sulfur, dual-doped carbon as high-performance metal-free oxygen electroreduction catalyst

    Nanomater Energy

    (2015)
  • H. Liu et al.

    Production of electricity during wastewater treatment using a single chamber microbial fuel cell

    Environ Sci Technol

    (2004)
  • H. Yuan et al.

    Oxygen reduction reaction catalysts used in microbial fuel cells for energy-efficient wastewater treatment: a review

    Materials Horizons

    (2016)
  • X.-W. Liu et al.

    Cathodic catalysts in bioelectrochemical systems for energy recovery from wastewater

    Chem Soc Rev

    (2014)
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