Review of high-performance biocathode using stainless steel and carbon-based materials in Microbial Fuel Cell for electricity and water treatment

Biocathode application in Microbial Fuel Cell (MFC) is a promising alternative for sustainable energy production. This recognition is due to its low construction and operation costs as well as the utilization of microbial metabolism in assisting power generation. One of the most crucial factors contributes to the performance of a biocathode MFC is the characteristics and configuration of the biocathode material itself. Hence it requires improvement for a better understanding towards its bioelectrochemical mechanisms as well as improving the MFC performance. However, reports on improving biocathode through support material selection and performance optimization in MFCs are still lacking. Based on previous reports, studies have shown that carbon-based material and stainless steel are possible biocathode materials for high power MFC performance. This review focuses on comparing these potential biocathode materials, regarding the commonly applied biocathode MFC designs and optimization. This review also compares the performance of biocathode materials in MFC based on the bioelectricity production and wastewater treatment. Further studies and understanding can provide a useful basis in fabricating biocathode designs and configurations to produce better sustainable bioelectricity in MFCs.     

Effect of ionic strength, cation exchanger and inoculum age on the performance of Microbial Fuel Cells

Power generation in Microbial fuel cells (MFCs) is a function of various physico-chemical as well as biological parameters. In this study, we have examined the effect of ionic strength, cation exchanger and inoculum age on power generation in a mediator MFC with methylene blue as electron mediator using Enterobacter cloacae IIT-BT08. The effect of ionic strength was studied using NaCl in the anode chamber of a two chambered salt-bridge MFC at concentrations of 5 mM, 10 mM and 15 mM. Maximum power density of 12.8 mW/m² was observed when 10 mM NaCl was used. Corresponding current density was noted to be 35.5 mA/m². Effect of cation exchanger was observed by replacing salt-bridge with a proton exchange membrane of equal surface area. When the salt-bridge was replaced by a proton exchange membrane, a 3-fold increase in the power density was observed. Power density and current density of 37.8 mW/m² and 110.3 mA/m² respectively were detected. The influence of the pre-inoculum on the MFC was studied using E. cloacae IIT-BT08 grown for 12, 14, 16 and 18 h. It was observed that 16 h grown culture when inoculated in the anode chamber gave the maximum power output. Power density and current density of 68 mW/m² and 168 mA/m² respectively were obtained. We demonstrate from these results that both physico-chemical as well as biological parameters need to be optimized for improving the power generation in MFCs.     

Low temperature processed composite cathodes for Solid-oxide fuel Cells

Low temperature processed composite cathodes for solid-state fuel cell (SOFC) have been developed, consisting of La_0.6Sr_0.4Ti_0.1Fe_0.9O₃ and Ag, as low as 800 °C process temperature. Using micro-tubular design, the performances of the cathodes have been investigated at the operating temperatures of 650 and 700 °C. The cell consists of NiO-Y stabilized zirconia (YSZ) as an anode (support tube), Sc stabilized zirconia (ScSZ) as an electrolyte, Gd doped ceria (GDC) for an inter-layer between the electrolyte and the cathodes. The single performance has varied depending upon the types of cathodes, and the composite cathode with 50 wt% La_0.6Sr_0.4Ti_0.1Fe_0.9O₃ and 50 wt% Ag has shown comparable performance to the cell with standard LSCF-GDC cathode.     

Steady-state performance and chemical efficiency of Microbial Electrolysis Cells

The objective of this paper was to study MEC performance at steady-state conditions in continuous mode and to analyse MEC performance in terms of chemical efficiency. At steady-state operation, a current density of 10.2 A m⁻² (applied voltage 1.0 V) for a set-up with an AEM was produced, compared to 7.2 A m⁻² for a set-up with a CEM. For all applied voltages, total internal resistance for the AEM configuration was lower than or the CEM configuration. Therefore, energy input for the AEM configuration is lower than for the CEM configuration. In case a CEM is used, the conductivity in the cathode reaches high values: >130 mS cm⁻¹. This conductivity is mainly caused by the presence of Na⁺ (7.8 g L⁻¹), K⁺ (12.2 g L⁻¹) and OH⁻ (8.3 g L⁻¹). Furthermore, MECs perform better at high buffer and electrolyte concentrations. However, as current density does not increase proportionally with increase in chemicals, the effectiveness of chemical addition decreases when more chemicals are added. Therefore, addition of chemicals and buffer does not necessarily enhance performance but increases operational costs.     

Influence and mechanism of dissolved oxygen on the performance of Ammonia-Oxidation Microbial Fuel Cell

Based on inorganic fuel, an Ammonia-Oxidation Microbial Fuel Cell (AO-MFC) had been developed, and the influence and mechanism of dissolved oxygen (DO) on the performance of nitrification and electricity generation were investigated. The results showed that the maximum conversion percentage of ammonium–nitrogen (NH₄⁺–N) was 99.7%. The output voltage and the power density were 98.5 ± 1.41 mV and 9.70 ± 0.27 mW m⁻² in the stable phase of electricity generation. In the AO-MFC, the electrons originated from ammonia and flowed to ammonia monooxygenase (AMO, which catalyzes the conversion of ammonia to hydroxylamine), Cyt aa₃ oxidase (which catalyzes the reduction of oxygen) and electrode, which were used for triggering ammonia oxidation, synthesizing ATP and generating electricity. Molecular oxygen played a key role in the electron distribution among these three acceptors. DO concentration too high (>6.45 mg L⁻¹) or too low (<0.5 mg L⁻¹) could exert a great negative influence on the performance of electricity generation.     

Performance of a scaled-up Microbial Fuel Cell with iron reduction as the cathode reaction

Scale-up studies of Microbial Fuel Cells are required before practical application comes into sight. We studied an MFC with a surface area of 0.5 m² and a volume of 5 L. Ferric iron (Fe³⁺) was used as the electron acceptor to improve cathode performance. MFC performance increased in time as a combined result of microbial growth at the bio-anode, increase in iron concentration from 1 g L⁻¹ to 6 g L⁻¹, and increased activity of the iron oxidizers to regenerate ferric iron. Finally, a power density of 2.0 W m⁻² (200 W m⁻³) was obtained. Analysis of internal resistances showed that anode resistance decreased from 109 to 7 mΩ m², while cathode resistance decreased from 939 to 85 mΩ m². The cathode was the main limiting factor, contributing to 58% of the total internal resistance. Maximum energy efficiency of the MFC was 41%.     

Experimental analysis of SO2 effects on Molten Carbonate Fuel Cells

The aim of this work is to investigate how SO₂ can affect MCFC performance and to discover the possible mechanisms involved in cathode sulphur poisoning, specifically considering the possible use of MCFCs in CCS (Carbon Capture and Storage) application. The different contributions of cathodic, anodic and electrolyte reactions have been considered to get a complete picture of the evolution of performance degradation. Experimental tests have been performed at the Fuel Cell Centre laboratories of Korea Institute of Science and Technology (KIST) thanks to 100 cm² single cell facilities and comparing results using both an optimized gas for laboratory conditions and a gas composition that simulates MCFCs when running in a Natural Gas Combined Cycle (NGCC) power plant. Polarisation curves, endurance tests, impedance measurements and gas analyses have been carried out to support the investigation.     

Electrode structure optimization combined with water feeding modes for Bi-Functional Unitized Regenerative Fuel Cells

Bi-functional Unitized Regenerative Fuel Cells (URFCs) based on proton-exchange membrane (PEM) electrolyte are promising in the field of energy storage. Their performance was investigated with catalyst loadings, carbon paper hydrophobicity and water feeding modes in both fuel cell (FC) and water electrolysis (WE) operations. The optimum membrane electrode assembly (MEA) is with 0.20 mg cm⁻² Pt (in 50% Pt/C catalyst) for the hydrogen electrode (HE), and a total catalyst loading of 0.80 mg cm⁻² for the oxygen electrode (OE). And its performance can reach 2.18 A cm⁻² at 1.80 V in WE test and 0.64 A cm⁻² at 0.60 V in FC test with air oxidant. Comparison of different carbon papers reveals that suitable hydrophobicity of OE carbon papers is obtained when the PTFE content accounts for 26.95 wt.%. Choice of water feeding modes, which has an influence on URFC performance in WE mode, is proven to have relations with current density and carbon paper hydrophobicity in a sophisticated way.     

Assessment of biotic and abiotic graphite cathodes for hydrogen production in microbial electrolysis cells

Hydrogen represents a promising clean fuel for future applications. The biocathode of a two-chambered microbial electrolysis cell (biotic MEC) was studied and compared with an abiotic cathode (abiotic MEC) in order to assess the influence of naturally selected microorganisms for hydrogen production in a wide range of cathode potentials (from −400 to −1800 mV vs SHE). Hydrogen production in both MECs increased when cathode potential was decreased. Microorganisms present in the biotic MEC were identified as Hoeflea sp. and Aquiflexum sp. Supplied energy was utilized more efficiently in the biotic MEC than in the abiotic, obtaining higher hydrogen production respect to energy consumption. At −1000 mV biotic MEC produced 0.89 ± 0.10 m³ H₂ d⁻¹ m⁻³NCC (Net Cathodic Compartment) at a minimum operational cost of 3.2 USD kg⁻¹ H₂. This cost is lower than the estimated market value for hydrogen (6 USD kg⁻¹ H₂).     

燃料电池技术发展及其成本

燃料电池是一种清洁、高效的发电方式，其普遍应用将会给人类带来极大的环境效益，解决人们目前所面对的能源缺乏问题。文章对燃料电池进行成本分析、预算，指出了实现燃料电池商业化存在的问题及相应的解决办法。同时，论述了ZAFC的成本及在交通运输中的应用，也对混合型交通工具的发展进行了分析，指出其在燃料电池发展过程中所起的作用和意义。     

Cathodic material effect on electron acceptance towards bioelectricity generation and wastewater treatment

Influence of cathode material on electron accepting conditions during the treatment of recalcitrant pharmaceutical wastewater (PWW) was comparatively evaluated at different organic loads (3, 6, 9 and 15 g/l) in three bioreactors. Two bio-electrochemical treatment systems employed with different electrode materials viz., BET-SS (graphite as anode and stainless steel (SS) as cathode) and BET-G (graphite as both anode and cathode) were evaluated for PWW degradation and bioelectricity generation in comparison to conventional anaerobic treatment (AnT). BET-G exhibited high bioelectrogenic activity than BET-SS, elucidating the impact of varied cathode material. High cathode potential necessary for effective reduction at cathode were observed with graphite-cathode than SS-cathode which are crucial for treatment and power generation. Ohmic losses ascribed to electrode material interference were relatively high in BET-SS in comparison to BET-G. Graphite-cathode exhibited high electron acceptance conditions leading to higher pollutant removal along with organic fraction degradation, bio-electrogenesis and inorganic salts removal, when compared to SS-cathode. Placement of electrode assembly while operating BET with different electrode materials is proved to be significant for treatment and bioelectricity production. Efficient electron accepting conditions and high cathode potential in BET-G proved graphite as promising cathode material over SS for the treatment of PWW.     

Synergetic interaction of magnetic field and loaded magnetite for enhanced acetate production in biocathode of microbial electrosynthesis system

Magnetic field (MF, 200 mT) and Fe₃O₄ (26 g/m²) are simultaneously employed to enhance acetate production from bicarbonate reduction in Serratia marcescens catalyzed cathode of microbial electrosynthesis system (MES), reaching 8.5 mM at an operational time of 9 d, higher than the controls by 1.7-time (Fe₃O₄ only), 1.8-fold (MF only), and 2.3-time (neither Fe₃O₄ nor MF). This confirms synergetic interaction of the MF and Fe₃O₄ for enhanced acetate production in the MES. The presence of MF and Fe₃O₄ induces the S. marcescens physiologically releasing more extracellular polymeric substances with a compositional diversity and containing more c-type cytochromes for facilitating extracellular electron transfer for efficient acetate production. Moreover, the favorable MF for less shedding (approximate 40%) of Fe₃O₄ from the biocathode, also contributes to the efficient MES. This study provides a feasible strategy of the Fe₃O₄ and MF for efficient acetate production from bicarbonate reduction in the MES.     

微生物燃料电池电能产生及污废水处理的研究进展

微生物燃料电池（microbial fuel cell, MFC）是采用微生物催化的电化学系统,可用于污废水处理领域。目前关于MFC的研究多集中在提高产电能力和去污效能方面。通过综述近期MFC的研究进展,建议该技术在污废水处理领域的研究重点放在产电微生物筛选培养、低成本电极材料修饰研发、调控MFC运行条件等方面,并应加强MFC与序批式反应器（sequencing batch reactor, SBR）、厌氧好氧（anoxic oxic, A/O）、膜生物反应器（membrane bio-reactor, MBR）等常见污废水处理工艺耦合联用的研究。     

车用加热器电磁燃油泵供油特性试验研究

介绍了车用加热器电磁燃油泵的结构和泵油原理。对影响电磁泵供油特性的油泵安装角度、泵油频率等因素进行了试验分析。提出了欠油容积概念,并认为泵油量主要受欠油容积和节流作用的影响,二者又受柱塞运行速度的影响,而速度又与泵油频率和重力有关,其实际作用于柱塞上的有效重力之大小又与电磁泵的安装角度有关。     

柴油机不同类型出油阀喷油特性的模拟与比较

随着柴油机高压喷射技术的广泛应用,喷油系统穴蚀的不规则喷射出现的可能性增加,为解决上述问题,由定容出油阀逐步发展出定压出油阀、阻尼出油阀、缓冲出油阀等．作者研究了国内外现有几种出油阀系统的边界条件及运动特性方程,开发了喷油特性通用计算程序INJECTION．文中比较了不同机型变工况下计算与实测的喷油特性,并运用程序分析了各种出油阀对喷油特性的影响．     

燃料电池发电的电站应用

燃料电池作为一种高效稳定的分布式清洁能源,其发电技术在电站领域的应用备受关注,而国内燃料电池电站尚在起步阶段,因此对这一领域的研究和实践经验具有重要意义。基于韩国燃气轮机联合循环电站中燃料电池发电项目的实施,介绍了燃料电池的选型,并通过模拟运行确定了最佳余热回收方案。MCFC燃料电池额定发电效率为47%,余热回收后效率提高3.5%。这些经验将对国内未来燃料电池电站的建设起到参考和借鉴意义。     

Photosynthetic microbial desalination cell (PhMDC) using Chlamydomonas sp. (UKM6) and Scenedesmus sp. (UKM9) as biocatalysts for electricity production and water treatment

A current Microbial Desalination Cell (MDC) system often uses chemicals or air cathodes that are toxic and impractical for scalable applications. This work presents the MDC performance that utilized microalgae species Chlamydomonas sp. (UKM6) and Scenedesmus sp. (UKM9). These species supported the role of the terminal electron acceptor in the cathode chamber of photosynthetic MDCs (PhMDC). The results showed that PhMDC-UKM9 and UKM6 produced 1942 mW/m³ and 1714 mW/m³ power densities with 44% and 32% desalination rates, respectively. The desalination of salt concentration (35 g/L) was approaching the practical application of seawater. Both UKM6 and UKM9 achieved chemical oxygen demand (COD) removal in the anode chamber by 49% and 53%, respectively. 16S microbial community analysis in anolyte revealed phylum Firmicutes as the dominion community. This study demonstrated that the local microalgae species integrate power production, wastewater treatment, and water purification through PhMDC operation, comparable with other studies using commercial microalgae.     

Improved ceramics leading to microtubular Solid Oxide Fuel Cells (mSOFCs)

Two methods for improving ceramics in SOFCs are contrasted: first, the strengthening of the cell materials through control of nanoparticle aggregation during ceramic processing; second, the design of tubular cells and stacks with smaller diameters to avoid thermal shock damage.