N-Doping of Graphene Aerogel as a Multifunctional Air Cathode for Microbial Fuel Cells

Polythiophene-Based Nonmetal Electrocatalyst with Biocompatibility to Boost Efficient CO2 Conversion

In a hybrid microbial-inorganic catalysis system, H2 evolution reaction (HER) electrocatalysts are coupled with microorganisms to achieve the highly efficient conversion of CO2 to value-added chemicals using H2 as an electron mediator. However, currently developed HER electrocatalysts suffer from poor biocompatibility, hindering the performance of the system. This study presents a N- and Si-doped polythiophene nanocomposite (PTh-NSi) as a nonmetal HER electrocatalyst with biocompatibility for use in a hybrid microbial-inorganic catalysis system. By coupling PTh-NSi with Ralstonia eutropha H16, conversion of CO2 to poly-β-hydroxybutyrate with a maximum yield of 662.99 ± 27.46 mg/L was achieved. The PTh-NSi electrocatalyst demonstrated HER performance in bacterial media, minimal reactive oxygen species production, and no heavy metal ion leaching, ensuring biocompatibility with R. eutropha H16. The interactions between PTh-NSi and R. eutropha H16 were revealed. This work highlights an approach to designing biocompatible catalysts for hybrid microbial-inorganic catalysis systems, offering the potential for sustainable CO2 conversion.

Bifunctional electrode materials: Enhancing microbial fuel cell efficiency with 3D hierarchical porous Fe3O4/Fe-N-C structures

The rational development of high-performance anode and cathode electrodes for microbial fuel cells (MFCs) is crucial for enhancing MFC performance. However, complex synthesis methods and single-performance electrode materials hinder their large-scale implementation. Here, three-dimensional hierarchical porous (3DHP) Fe3O4/Fe-N-C composites were prepared via the hard template method. Notably, Fe3O4/Fe-N-C-0.04-600 demonstrated uniformly dispersed Fe3O4 nanoparticles and abundant Fe-Nx and pyridinic nitrogen, showing excellent catalytic performance for oxygen reduction reaction (ORR) with a half-wave potential (E1/2) of 0.74 V (vs. RHE), surpassing Pt/C (0.66 V vs. RHE). Moreover, Fe3O4/Fe-N-C-0.04-600 demonstrated favorable biocompatibility as an anode material, enhancing anode biomass and extracellular electron transfer efficiency. Sequencing results confirmed its promotion of electrophilic microorganisms in the anode biofilm. MFCs employing Fe3O4/Fe-N-C-0.04-600 as both anode and cathode materials achieved a maximum power density of 831.8 ± 27.7 mW m-2, enduring operation for 38 days. This study presents a novel approach for rational MFC design, emphasizing bifunctional materials capable of serving as anode materials for microorganism growth and as cathode catalysts for ORR catalysis.

Controlling N-Doping Nature at Carbon Aerogels from Biomass for Enhanced Oxygen Reduction in Seawater Batteries

Pyridinic N-type doped at carbon has been known to have better electrocatalytic activity toward the oxygen reduction reaction (ORR) than the others. Herein, we proposed to prepare pyridinic N doped at carbon aerogels (CaA) derived from biomass, i.e., coir fiber (CF) and palm empty fruit bunches (PEFBs), by adjusting the pyrolysis temperature during carbonization of the biomass-based-cellulose aerogels. The cellulose aerogels were prepared by the ammonia-urea system as the cellulose solvent, in which ammonia also acted as a N source for doping and urea as the cellulose cross-linker. The as-prepared cellulose aerogels were directly pyrolyzed to produce N-doped CaA. It was found that the type of N doping is dominated by pyrrolic N at pyrolysis temperature of 600 °C, pyridinic N at 700 °C, and graphitic N at 800 °C. The pyridinic N exhibited better performance as an electrocatalyst for the ORR than pyrrolic N and graphitic N. The ORR using pyridinic N follows the four-electron pathway, which quantitatively implies a more electrochemically stable process. When used as a cathode for the Mg-air battery using a 3.5% NaCl electrolyte, the pyridinic N CaA exhibited excellent performance by giving a cell voltage of approximately 1.1 V and delivered a high discharge capacity of 411.64 mA h g-1 for CF and 492.64 mA h g-1 for PEFB corresponding to an energy density of 464.23 and 529.49 mW h g-1, respectively.

Environmental biotechnology and the involving biological process using graphene-based biocompatible material

Biotechnology is a promising approach to environmental remediation but requires improvement in efficiency and convenience. The improvement of biotechnology has been illustrated with the help of biocompatible materials as biocarrier for environmental remediations. Recently, graphene-based materials (GBMs) have become promising materials in environmental biotechnology. To better illustrate the principle and mechanisms of GBM application in biotechnology, the comprehension of the biological response of microorganisms and enzymes when facing the GBMs is needed. The review illustrated distinct GBM-microbe/enzyme composites by providing the GBM-microbe/enzyme interaction and the determining factors. There are diverse GBM modifications for distinct biotechnology applications. Each of these methods and applications depends on the physicochemical properties of GBMs. The applications of these composites were mainly categorized as pollutant adsorption, anaerobic digestion, microbial fuel cells, and organics degradation. Where information was available, the strategies and mechanisms of GBMs in improving application efficacies were also demonstrated. In addition, the biological response, from microbial community changes, extracellular polymeric substances changes to biological pathway alteration, may become important in the application of these composites. Furthermore, we also discuss challenges facing the environmental application of GBMs, considering their fate and toxicity in the ecosystem, and offer potential solutions. This research significantly enhances our comprehension of the fundamental principles, underlying mechanisms, and biological pathways for the in-situ utilization of GBMs.

A Review of Nitrogen-Doped Graphene Aerogel in Electromagnetic Wave Absorption

Graphene aerogels (GAs) possess a remarkable capability to absorb electromagnetic waves (EMWs) due to their favorable dielectric characteristics and unique porous structure. Nevertheless, the introduction of nitrogen atoms into graphene aerogels can result in improved impedance matching. In recent years, nitrogen-doped graphene aerogels (NGAs) have emerged as promising materials, particularly when combined with magnetic metals, magnetic oxides, carbon nanotubes, and polymers, forming innovative composite systems with excellent multi-functional and broadband absorption properties. This paper provides a comprehensive summary of the synthesis methods and the EMW absorption mechanism of NGAs, along with an overview of the absorption properties of nitrogen-doped graphene-based aerogels. Furthermore, this study sheds light on the potential challenges that NGAs may encounter. By highlighting the substantial contribution of NGAs in the field of EMW absorption, this study aims to facilitate the innovative development of NGAs toward achieving broadband absorption, lightweight characteristics, and multifunctionality.

Gd-Co nanosheet arrays coated on N-doped carbon spheres as cathode catalyst in photosynthetic microalgae microbial fuel cells

Biocompatible, durable and high catalytic cathode is crucial for the performance of photosynthetic microalgae microbial fuel cell (PMMFC). In this study, gadolinium-cobalt (Gd-Co) nanosheet arrays were coated on N-doped carbon spheres (N-CSs) that were supported using nickel foam (NF), to form a unique 3D hierarchical architecture of Gd-Co@N-CSs/NF cathode material. The morphology and structure of Gd-Co@N-CSs/NF was investigated by physicochemical characterization. The electricity generation and stability of NF, N-CSs/NF, Co@N-CSs/NF and Gd-Co@N-CSs/NF were evaluated using a dual-chamber PMMFC system with Chlorella vulgaris (C. vulgaris) in the cathode chamber. Results showed that doption of Gd to the cathode material resulted in Gd-Co@N-CSs/NF exhibiting superior catalytic activity for the oxygen reduction reaction (ORR), with an ORR peak potential of 0.78 V (vs. RHE). The electron transfer number (n) of Gd-Co@N-CSs/NF was 3.906, indicating ORR was mainly realized via 4e^- transfer pathway. Gd-Co@N-CSs/NF achieved a maximum power density of 115.9 mW m^-2 and an open circuit voltage of 614.8 mV, higher than the other three cathode materials. Gd-Co@N-CSs/NF exhibited excellent stability during 360 h of the PMMFC process, only dropping 5.8 % of maximum voltage. The cell density of C. vulgaris (3.7 × 10¹⁰ cells L^-1) in Gd-Co@N-CSs/NF system was significantly higher than those of NF, N-CSs/NF and Co@N-CSs/NF. This study shows that Gd-Co@N-CSs/NF is a promising cathode material and may be highly beneficial for the enhancement of PMMFC systems.