High‐Performance Silver Cathode Surface Treated with Scandia‐Stabilized Zirconia Nanoparticles for Intermediate Temperature Solid Oxide Fuel Cells

This work introduces a novel silver composite cathode with a surface coating of scandia‐stabilized zirconia (ScSZ) nanoparticles for application in intermediate temperature solid oxide fuel cells (IT‐SOFCs). The ScSZ coating is expected to maximize the triple boundary area of the Ag electrode, ScSZ electrolyte, and oxygen gas, where the oxygen reduction reaction occurs. The coating also protects the porous Ag against thermal agglomeration during fuel cell operation. The ScSZ nanoparticles are prepared by sputtering scandium‐zirconium alloy followed by thermal oxidation on Ag mesh. The performance of the solid oxide fuel cells with a gadolinia‐doped ceria electrolyte support is evaluated. At temperatures <500 °C, our optimized Ag‐ScSZ cathode outperforms the bare Ag cathode and even the platinum cathode, which has been believed to be the best material for this purpose. The highest cell peak power with the Ag‐ScSZ cathode is close to 60 mW cm^?2 at 450 °C, while bare Ag and optimized Pt cathodes produce 38.3 and 49.4 mW cm^?2, respectively. Long‐term current measurement also confirms that the Ag‐ScSZ cathode is thermally stable, with less degradation than bare Ag or Pt.     

Performance and microbial ecology of air-cathode microbial fuel cells with layered electrode assemblies

Microbial fuel cells (MFCs) can be built with layered electrode assemblies, where the anode, proton exchange membrane (PEM), and cathode are pressed into a single unit. We studied the performance and microbial community structure of MFCs with layered assemblies, addressing the effect of materials and oxygen crossover on the community structure. Four MFCs with layered assemblies were constructed using Nafion or Ultrex PEMs and a plain carbon cloth electrode or a cathode with an oxygen-resistant polytetrafluoroethylene diffusion layer. The MFC with Nafion PEM and cathode diffusion layer achieved the highest power density, 381 mW/m² (20 W/m³). The rates of oxygen diffusion from cathode to anode were three times higher in the MFCs with plain cathodes compared to those with diffusion-layer cathodes. Microsensor studies revealed little accumulation of oxygen within the anode cloth. However, the abundance of bacteria known to use oxygen as an electron acceptor, but not known to have exoelectrogenic activity, was greater in MFCs with plain cathodes. The MFCs with diffusion-layer cathodes had high abundance of exoelectrogenic bacteria within the genus Geobacter. This work suggests that cathode materials can significantly influence oxygen crossover and the relative abundance of exoelectrogenic bacteria on the anode, while PEM materials have little influence on anode community structure. Our results show that oxygen crossover can significantly decrease the performance of air-cathode MFCs with layered assemblies, and therefore limiting crossover may be of particular importance for these types of MFCs.     

Enhancing substrate utilization and power production of a microbial fuel cell with nitrogen-doped carbon aerogel as cathode catalyst

Objectives

Catalytic efficiency of a nitrogen-doped, mesoporous carbon aerogel cathode catalyst was investigated in a two-chambered microbial fuel cell (MFC) applying graphite felt as base material for cathode and anode, utilizing peptone as carbon source.

Results

This mesoporous carbon aerogel containing catalyst layer on the cathode increased the maximum power density normalized to the anode volume to 2.7 times higher compared to the maximum power density obtained applying graphite felt cathode without the catalyst layer. At high (2 and 3) cathode/anode volume ratios, maximum power density exceeded 40 W m^?3. At the same time, current density and specific substrate utilization rate increased by 58% resulting in 31.9 A m^?3 and 18.8 g COD m^?3 h^?1, respectively (normalized to anode volume). Besides the increase of the power and the rate of biodegradation, the investigated catalyst decreased the internal resistance from the range of 450–600 to 350–370 Ω.

Conclusions

Although Pt/C catalyst proved to be more efficient, a considerable decrease in the material costs might be achieved by substituting it with nitrogen-doped carbon aerogel in MFCs. Such cathode still displays enhanced catalytic effect.

     

Application of Co-naphthalocyanine (CoNPc) as alternative cathode catalyst and support structure for microbial fuel cells

Co-naphthalocyanine (CoNPc) was prepared by heat treatment for cathode catalysts to be used in microbial fuel cells (MFCs). Four different catalysts (Carbon black, NPc/C, CoNPc/C, Pt/C) were compared and characterized using XPS, EDAX and TEM. The electrochemical characteristics of oxygen reduction reaction (ORR) were compared by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The Co-macrocyclic complex improves the catalyst dispersion and oxygen reduction reaction of CoNPc/C. The maximum power of CoNPc/C was 64.7 mW/m² at 0.25 mA as compared with 81.3 mW/m² of Pt/C, 29.7 mW/m² of NPc/C and 9.3 mW/m² of carbon black when the cathodes were implemented in H-type MFCs. The steady state cell, cathode and anode potential of MFC with using CoNPc/C were comparable to those of Pt/C.     

Sb‐Doped SnO2 Hollow Spheres Offering Micro‐ and Nanoporosity in Fuel Cell Electrode Structures

Sb‐doped SnO₂ (ATO) is used as an alternative support material to replace carbon in the highly corrosive environment of a fuel cell cathode. Two ATO powders with different morphologies are decorated with Pt nanoparticles and afterwards used as the cathode catalyst. The commercial ATO powder exhibits crystallites in the nanometer range, while the home‐made ATO powder, which was synthesized by ultrasonic spray pyrolysis, consists of polycrystalline hollow spheres. The spheres have diameters in the micrometer range and are composed of individual nanocrystallites. The unusual morphology of the home‐made ATO offers nano‐ and microporosity at the same time and opens up new possibilities for the controlled design of electrode structures in low‐temperature polymer electrolyte fuel cells. Both materials are characterized by XRD, SEM, and TEM and tested in a single cell set‐up. While almost no current is gained from the membrane electrode assembly with the commercial ATO support, the cell with the home‐made ATO achieves a mediocre performance. This higher activity, however, is obtained with approximately half the Pt content compared to the catalyst with the commercial support. The different behaviours of both ATO powders can therefore mainly be attributed to differences in the specific support morphology.     

Air-cathode structure optimization in separator-coupled microbial fuel cells

Microbial fuel cells (MFC) with 30% wet-proofed air cathodes have previously been optimized to have 4 diffusion layers (DLs) in order to limit oxygen transfer into the anode chamber and optimize performance. Newer MFC designs that allow close electrode spacing have a separator that can also reduce oxygen transfer into the anode chamber, and there are many types of carbon wet-proofed materials available. Additional analysis of conditions that optimize performance is therefore needed for separator-coupled MFCs in terms of the number of DLs and the percent of wet proofing used for the cathode. The number of DLs on a 50% wet-proofed carbon cloth cathode significantly affected MFC performance, with the maximum power density decreasing from 1427 to 855 mW/m² for 1–4 DLs. A commonly used cathode (30% wet-proofed, 4 DLs) produced a maximum power density (988 mW/m²) that was 31% less than that produced by the 50% wet-proofed cathode (1 DL). It was shown that the cathode performance with different materials and numbers of DLs was directly related to conditions that increased oxygen transfer. The coulombic efficiency (CE) was more affected by the current density than the oxygen transfer coefficient for the cathode. MFCs with the 50% wet-proofed cathode (2 DLs) had a CE of >84% (6.8 A/m²), which was substantially larger than that previously obtained using carbon cloth air-cathodes lacking separators. These results demonstrate that MFCs constructed with separators should have the minimum number of DLs that prevent water leakage and maximize oxygen transfer to the cathode.     

Activity and stability of pyrolyzed iron ethylenediaminetetraacetic acid as cathode catalyst in microbial fuel cells

A low-cost and effective iron-chelated catalyst was developed as an electrocatalyst for the oxygen reduction reaction (ORR) in microbial fuel cells (MFCs). The catalyst was prepared by pyrolyzing carbon mixed iron-chelated ethylenediaminetetraacetic acid (PFeEDTA/C) in an argon atmosphere. Cyclic voltammetry measurements showed that PFeEDTA/C had a high catalytic activity for ORR. The MFC with a PFeEDTA/C cathode produced a maximum power density of 1122 mW/m², which was close to that with a Pt/C cathode (1166 mW/m²). The PFeEDTA/C was stable during an operation period of 31 days. Based on X-ray diffraction and X-ray photoelectron spectroscopy measurements, quaternary-N modified with iron might be the active site for the oxygen reduction reaction. The total cost of a PFeEDTA/C catalyst was much lower than that of a Pt catalyst. Thus, PFeEDTA/C can be a good alternative to Pt in MFC practical applications.     

A Highly Order‐Structured Membrane Electrode Assembly with Vertically Aligned Carbon Nanotubes for Ultra‐Low Pt Loading PEM Fuel Cells

A simple method was developed to prepare ultra‐low Pt loading membrane electrode assembly (MEA) using vertically aligned carbon nanotubes (VACNTs) as highly ordered catalyst support for PEM fuel cells application. In the method, VACNTs were directly grown on the cheap household aluminum foil by plasma enhanced chemical vapor deposition (PECVD), using Fe/Co bimetallic catalyst. By depositing a Pt thin layer on VACNTs/Al and subsequent hot pressing, Pt/VACNTs can be 100% transferred from Al foil onto polymer electrolyte membrane for the fabrication of MEA. The whole transfer process does not need any chemical removal and destroy membrane. The PEM fuel cell with the MEA fabricated using this method showed an excellent performance with ultra‐low Pt loading down to 35 μg cm^?2 which was comparable to that of the commercial Pt catalyst on carbon powder with 400 μg cm^?2. To the best of our knowledge, for the first time, we identified that it is possible to substantially reduce the Pt loading one order by application of order‐structured electrode based on VACNTs as Pt catalysts support, compared with the traditional random electrode at a comparable performance through experimental and mathematical methods.     

Iron phthalocyanine supported on amino-functionalized multi-walled carbon nanotube as an alternative cathodic oxygen catalyst in microbial fuel cells

Amino-functionalized multi-walled carbon nanotube (a-MWCNT)-supported iron phthalocyanine (FePc) (a-MWCNT/FePc) has been investigated as a catalyst for the oxygen reduction reaction (ORR) in an air-cathode single-chambered microbial fuel cell (MFC). Cyclic and linear sweep voltammogram are employed to investigate the electrocatalytic activity of the a-MWCNT/FePc for ORR. The maximum power density of 601 mW m⁻² is achieved from a MFC with the a-MWCNT/FePc cathode, which is the highest energy output compared to those MFCs with other materials supported FePc, such as carbon black, pristine MWCNT (p-MWCNT), carboxylic acid functionalized MWCNT (c-MWCNT), and even with a Pt/C cathode. Furthermore, cyclic voltammetry performed on the a-MWCNT/FePc electrode suggests that the a-MWCNT/FePc has an electrochemical activity for ORR via a four-electron pathway in a neutral pH solution. This work provides a potential alternative to Pt in MFCs for sustainable energy generation.     

Superior Oxygen Reduction Reaction on Phosphorus‐Doped Carbon Dot/Graphene Aerogel for All‐Solid‐State Flexible Al–Air Batteries

Carbon dots have been recognized as one of the most promising candidates for the oxygen reduction reaction (ORR) in alkaline media. However, the desired ORR performance in metal–air batteries is often limited by the moderate electrocatalytic activity and the lack of a method to realize good dispersion. To address these issues, herein a biomass‐deriving method is reported to achieve the in situ phosphorus doping (P‐doping) of carbon dots and their simultaneous decoration onto graphene matrix. The resultant product, namely P‐doped carbon dot/graphene (P‐CD/G) nanocomposites, can reach an ultrahigh P‐doping level for carbon nanomaterials. The P‐CD/G nanocomposites are found to exhibit excellent ORR activity, which is highly comparable to the commercial Pt/C catalysts. When used as the cathode materials for a primary liquid Al–air battery, the device shows an impressive power density of 157.3 mW cm^?2 (comparing to 151.5 mW cm^?2 of a similar Pt/C battery). Finally, an all‐solid‐state flexible Al–air battery is designed and fabricated based on our new nanocomposites. The device exhibits a stable discharge voltage of ≈1.2 V upon different bending states. This study introduces a unique biomass‐derived material system to replace the noble metal catalysts for future portable and wearable electronic devices.     

Effects of sulfide on microbial fuel cells with platinum and nitrogen-doped carbon powder cathodes

Because of the advantages of low cost, good electrical conductivity and high oxidation resistance, nitrogen-doped carbon (NDC) materials have a potential to replace noble metals in microbial fuel cells (MFCs) for wastewater treatment. In spite of a large volume of studies on NDC materials as catalysts for oxygen reduction reaction, the influence of sulfide on NDC materials has not yet been explicitly reported so far. In this communication, nitrogen-doped carbon powders (NDCP) were prepared by treating carbon powders in nitric acid under reflux condition. Sodium sulfide (Na(2)S) was added to the cathodic electrolyte to compare its effects on platinum (Pt) and NDCP cathodes. Cell voltages, power density and cathodic potentials were monitored without and with Na(2)S and after Na(2)S was removed. The maximum cell voltage of the MFCs with Pt cathode decreased by 10% in the presence of Na(2)S that did not change the performance of the MFC with NDCP cathode, and the maximum power density of the MFC with NDCP cathode was even 11.3% higher than that with Pt cathode (222.5 ± 8 mW m(-2) vs. 199.7 ± 4 mW m(-2)).     

Development of Highly Stable and Mass Transfer‐Enhanced Cathode Catalysts: Support‐Free Electrospun Intermetallic FePt Nanotubes for Polymer Electrolyte Membrane Fuel Cells

Proton exchange membrane fuel cells (PEMFCs) are an alternative clean energy source and they are attracting increased attention. However, several limitations such as degradation of the carbon support and Nafion ionomer in the cathode electrode must be overcome for practical applications of PEMFCs. Support‐free 1D‐ordered intermetallic nanotubes (NTs) are considered as promising candidates for highly active and durable cathode catalysts in PEMFCs. However, 1D nanotubes are difficult to produce at large scale because they have generally been synthesized using a template‐based method that requires multistep synthetic routes. Herein, a simple and scalable method to produce ordered‐intermetallic FePt nanotubes by electrospinning is reported. When tested as cathode catalysts, under the US Department of Energy's reference condition, the activity of face‐centered‐tetragonal (fct) FePt NTs surpasses that of commercial Pt/C. In an accelerated degradation test at 1.4 V for 3 h, the degradation activity rate of fct‐FePt NTs is only 10%, whereas that of commercial Pt/C catalysts is 65%. For practical PEMFCs, this approach would provide simple routes to support‐free intermetallic nanotube structures with superior kinetic activity and higher durability than those of commercial Pt/C catalyst.     

Biomass‐Derived 3D Carbon Aerogel with Carbon Shell‐Confined Binary Metallic Nanoparticles in CNTs as an Efficient Electrocatalyst for Microfluidic Direct Ethylene Glycol Fuel Cells

Flexible and 3D carbon aerogels (CAs) composed of carbon nanotubes (CNTs) with carbon shell‐confined binary palladium–nickel (Pd_x–Ni_y) nanocatalysts on carbon fibers (Pd_x–Ni_y/NSCNT/CA) have been developed through a facile chemical vapor deposition method. The 3D porous carbon network and the synergistic effect of carbon shell‐confined bimetal nanoparticles of rationally constructed aerogels facilitate enhanced electrocatalytic and antipoisoning activities toward ethylene glycol (EG) oxidation reaction compared to the commercial Pt/C catalyst. With the 3D morphological features and direct growth of Pd–Ni bimetallic nanoparticles encapsulated CNTs on carbon fibers, the Pd₅₂–Ni₄₈/NSCNT/CA delivers a maximum microfluidic direct ethylene glycol fuel cell (µDEGFC) power density and durability of, respectively, 62.8 mW cm^?2 and 60 h. The superior performance observed, with Pd₅₂–Ni₄₈/NSCNT/CA amongst the catalysts reported in the literature, opens an exciting research avenue towards powering next‐generation, portable electronics.     

Construction and operation of freshwater sediment microbial fuel cell for electricity generation

In this work, sediment microbial fuel cell (SMFC) with granule activated carbon (GAC) cathode and stainless steel anode was constructed in laboratory tests and various factors on SMFC power output were investigated. The maximum power densities for the SMFC with GAC cathode was 3.5 mW m⁻², it was much higher than SMFC with round stainless steel cathode. Addition of cellulose reduced the output power from SMFC at the beginning of experiments, while the output power was found to increase after adding cellulose to sediments on day 90 of operation. On 160 day, maximum power density from the SMFC with adding 0.2% cellulose reached to 11.2 mW m⁻². In addition, the surface morphology of stainless steel anode on day 90 was analyzed by scanning electron microscope. It was found that the protection layer of the stainless steel as electrode in SMFCs was destroyed to some extent.     

Treatment of fruit waste leachate using microbial fuel cell: Preservation of agricultural environment

A microbial fuel cell (MFC) was conceived to low electric power production in parallel to valorization of industrial wastes and environment preservation. It consisted of two compartments separated by polymer Nafion membrane, platinum grid as cathode catalyst and graphite rod inoculated with fruit leachate as bio-anode. Owing to its bio-compatibity with bacterial inoculum and chemical stability, Graphite Carbon (GC) was tested as carrier of biofilm using fruit waste inoculum. The maximum power density harvested with this electrode was about 20 mW.m^?2 much greater than that obtained previously with a garden compost inoculum (i.e. 7 mW.m^?2). The difference between the two values may be attributed to the bacterial nature of inoculum utilized. Impressively, upon the addition of 6 mL of fuel (sucrose), the soft porous graphite felt GF yielded voltage (260 mV) which was significantly higher than that of the hard smooth solid GC (i.e. 140 mV). This result makes in evidence the effect of adsorption of the electro-active biofilm onto the surface of the electrode. We ascribe therefore the enhanced power density to a more uniform spread out of the electro-active biofilm within the GF matrix, as verified by higher conductivity obtained with four probe method. The results reported herein highlight the importance of assessing the bio-catalytic activity towards the oxidation of the organic substrate to yield renewable low energy. The experimental data and the differences between the bio-anodes GC and GF were discussed in term of electrochemical techniques such as cyclic voltammetry, impedance spectroscopy and four-probe conductivity. Whatever the nature of the bio-anodes, the overall bacterial colonization still yields low values of clean electric energy compared to highly polluted energy obtained with an alkaline fuel cell.     

Simultaneous carbon and nitrogen removal from piggery wastewater using loop configuration microbial fuel cell

Simultaneous carbon and nitrogen removal using loop configuration microbial fuel cell (MFC) with relatively large size of 5 L was investigated in this study. Four MFC reactors were constructed with a loop configuration to eliminate the pH gradient, and the reactor performance was examined with different separators and cathode materials. The performance of the reactors in terms of electricity generation and contaminant removal rate was examined. Results showed that a maximum power density of 1415.6 mW/m³ (The empty bed volume of anode chamber) was obtained at a current density of 3258.5 mA/m³ with cation exchange membrane as separator and graphite felt (Pt coated) as cathode using the piggery wastewater as feed, and the organic removal rate obtained was approximately 0.523 kg COD/m³/d (total anode chamber) with nitrogen removal rate of 0.194 kg N/m³/d (total cathode chamber).     

Effect of vitamins and cell constructions on the activity of microbial fuel cell battery

Construction of efficient performance of microbial fuel cells (MFCs) requires certain practical considerations. In the single chamber microbial fuel cell, there is no border between the anode and the cathode, thus the diffusion of the dissolved oxygen has a contrary effect on the anodic respiration and this leads to the inhibition of the direct electron transfer from the biofilm to the anodic surface. Here, a fed-batch single chambered microbial fuel cells are constructed with different distances 3 and 6?cm (anode- cathode spacing), while keeping the working volume is constant. The performance of each MFC is individually evaluated under the effects of vitamins & minerals with acetate as a fed load. The maximum open circuit potential during testing the 3 and 6?cm microbial fuel cells is about 946 and 791?mV respectively. By decreasing the distance between the anode and the cathode from 6 to 3?cm, the power density is decreased from 108.3?mW?m^?2 to 24.5?mW?m^?2. Thus, the short distance in membrane-less MFC weakened the cathode and inhibited the anodic respiration which affects the overall performance of the MFC efficiency. The system is displayed a maximum potential of 564 and 791?mV in absence & presence of vitamins respectively. Eventually, the overall functions of the acetate single chamber microbial fuel cell can be improved by the addition of vitamins & minerals and increasing the distance between the cathode and the anode.     

A Conductive Molecular Framework Derived Li2S/N,P‐Codoped Carbon Cathode for Advanced Lithium–Sulfur Batteries

Li₂S is one of the most promising cathode materials for Li‐ion batteries because of its high theoretical capacity and compatibility with Li‐metal‐free anode materials. However, the poor conductivity and electrochemical reactivity lead to low initial capacity and severe capacity decay. In this communication, a nitrogen and phosphorus codoped carbon (N,P–C) framework derived from phytic acid doped polyaniline hydrogel is designed to support Li₂S nanoparticles as a binder‐free cathode for Li–S battery. The porous 3D architecture of N and P codoped carbon provides continuous electron pathways and hierarchically porous channels for Li ion transport. Phosphorus doping can also suppress the shuttle effect through strong interaction between sulfur and the carbon framework, resulting in high Coulombic efficiency. Meanwhile, P doping in the carbon framework plays an important role in improving the reaction kinetics, as it may help catalyze the redox reactions of sulfur species to reduce electrochemical polarization, and enhance the ionic conductivity of Li₂S. As a result, the Li₂S/N,P–C composite electrode delivers a stable capacity of 700 mA h g^?1 with average Coulombic efficiency of 99.4% over 100 cycles at 0.1C and an areal capacity as high as 2 mA h cm^?2 at 0.5C.     

All‐Organic Battery Composed of Thianthrene‐ and TCAQ‐Based Polymers

An all‐organic battery consisting of two redox‐polymers, namely poly(2‐vinylthianthrene) and poly(2‐methacrylamide‐TCAQ) is assembled. This all‐organic battery shows excellent performance characteristics, namely flat discharge plateaus, an output voltage exceeding 1.3 V, and theoretical capacities of both electrodes higher than 100 mA h g^?1. Both organic electrode materials are synthesized in two respective three synthetic steps using the free‐radical polymerization technique. Li‐organic batteries manufactured from these polymers prove their suitability as organic electrode materials. The cathode material poly(2‐vinylthianthrene) (3) displays a discharging plateau at 3.95 V versus Li⁺/Li and a discharge capacity of 105 mA h g^?1, corresponding to a specific energy of about 415 mW h g^?1. The anode material poly(2‐methacrylamide‐TCAQ) (7) exhibits an initial discharge capacity of 130 mA h g^?1, corresponding to 94% material activity. The combination of both materials results in an all‐organic battery with a discharge voltage of 1.35 V and an initial discharge capacity of 105 mA h g^?1 (95% material activity).     

Unravelling Degradation Pathways of Oxide‐Supported Pt Fuel Cell Nanocatalysts under In Situ Operating Conditions

Knowledge of degradation pathways of catalyst/support ensembles aids the development of rational strategies to improve their stability. Here, this is exemplified using indium tin oxide (ITO)‐supported Platinum nanoparticles as electrocatalysts at fuel cell (FC) cathodes under degradation protocols to mimic operating conditions in two potential regimes. The evolution of crystal structure, composition, crystallite and particle size is tracked by in situ X‐ray techniques (small and wide angle scattering), metal dissolution by in situ scanning flow cell coupled with mass spectrometry (SFC ICP‐MS) and Pt surface morphology by advanced electron microscopy. In a regular FC operation regime, Pt poisoning rather than Pt particle growth, agglomeration, dissolution or detachment was found to be the likely origin of the observed degradation and ORR activity losses. In the start‐up regime degradation is actually suppressed and only minor losses in catalytic activity are observed. The presented data thus highlight the excellent nanoparticle stabilization and corrosion resistance of the ITO support, yet point to a degradation pathway involving Pt surface modifications by deposition of sub‐monolayers of support metal ions. The identified degradation pathway of the Pt/oxide catalyst/support couple contributes to our understanding of cathode electrocatalysts for polymer electrolyte fuel cells (PEFC).