Fabrication and evaluation of passive alkaline membraneless microfluidic DMFC

The fabrication and evaluation of a passive, air-breathing, membraneless microfluidic direct methanol fuel cell (ML-μDMFC) using a methanol-tolerant Ag/Pt/CP cathode is presented here. We previously proposed that due to its high tolerance to methanol and the good activity towards the oxygen reduction reaction in alkaline medium, this catalyst could be useful to reduce the methanol crossover effect in direct methanol fuel cells. Therefore, in order to demonstrate it, we designed and fabricated a microfluidic device that allowed the evaluation of the cathode in a high fuel concentration environment, using up to 5 M MeOH in 0.5 M KOH in passive mode. The results confirmed the high tolerance to MeOH and the ORR selectivity of the Ag/Pt/CP cathode, in contrast with a Pt/CP cathode, where performance decreased severely due to the methanol crossover. Employing the methanol-tolerant cathode, it was possible to obtain a power density of 2.4 mW cm⁻². Additionally, the durability studies revealed more stability for the ML-μDMFC using the bimetallic catalyst, compared with Pt/CP.     

Manganese dioxide as a cathode catalyst for a direct alcohol or sodium borohydride fuel cell with a flowing alkaline electrolyte

The oxygen reduction reaction at a manganese dioxide cathode in alkaline medium is studied using cyclic voltammetry and by measuring volume of oxygen consumed at the cathode. The performance of the manganese dioxide cathode is also determined in the presence of fuel and an alkali mixture with a standard Pt/Ni anode in a flowing alkaline-electrolyte fuel cell. The fuels tested are methanol, ethanol and sodium borohydride (1 M), while 3 M KOH is used as the electrolyte. The performance of the fuel cell is measured in terms of open-circuit voltage and current–potential characteristics. A single peak in the cyclic voltammogram suggests that a four-electron pathway mechanism prevails during oxygen reduction. This is substantiated by calculating the number of electrons involved per molecule of oxygen that are reacted at the MnO₂ cathode from the oxygen consumption data for different fuels. The results show that the power density of the fuel cell increases with increase in MnO₂ loading to a certain limit but then decreases with further loading. The maximum power density is obtained at 3 mg cm⁻² of MnO₂ for each of the three different fuels.     

Tin-nitrogen/carbon for superior oxygen reduction reaction at fuel cell cathode

This work reports on the synthesis of tin-nitrogen/carbon (Sn–N/C) catalysts suitable for the electroreduction of molecular oxygen at the cathode of proton exchange membrane fuel cells. The catalysts were synthesized through a simple pyrolysis process of folic acid as the carbon and nitrogen source, tin chloride as a tin source and Vulcan carbon as the substrate. The synthesized catalyst exhibited excellent oxygen reduction activity with a half wave potential of 0.82 V and a mass activity of 15.5 mA mg⁻¹. Successful application at the cathode of a self-breathing fuel cell further confirmed the superior performance of this catalyst leading to a power density of 29.4 mW cm⁻². This is very comparable to the reference platinum/Vulcan carbon catalyst (28.4 mW cm⁻²). In addition, this Sn–N/C catalyst showed good stability under accelerated stress tests with only a 12% decrease in fuel cell performance after 10,000 cycles. The superior performance was assumed to be due to the presence of both metal-nitrogen and nitrogen-carbon active sites, which facilitate the four-electron path of the oxygen reduction reaction.     

Enhanced bioelectricity generation and cathodic oxygen reduction of air breathing microbial fuel cells based on MoS2 decorated carbon nanotube

Increasing efforts have been devoted to enhancing the cathode activity towards oxygen reduction and improve power generation of air breathing microbial fuel cells. Exploring non-precious metal and highly active cathodic catalyst plays a key role in improving cathode performance. Our work aims to investigate the electrocatalyst behavior and power output of the single-chamber MFC equipped with carbon nanotubes hybridized molybdenum disulfide nanocomposites (CNT/MoS₂) cathode. MoS₂ nanosheets embedded into the CNTs network structure is synthesized by a facile hydrothermal method. The CNT/MoS₂-MFC achieves a maximum power density of 53.0 mW m⁻², which is much higher than those MFCs with pure CNTs (21.4 mW m⁻²) or solely MoS₂ (14.4 mW m⁻²) cathode. The oxygen reduction reaction (ORR) test also demonstrates a promoted electrocatalytic activity of synthesized material, which may be attributed to the special interlaced structure and abundant oxygen chemisorption sites of CNT/MoS₂. Such CNTs-based noble-metal-free catalyst presents a new approach to the application of MFCs cathode materials.     

Evaluation of carbon supported Fe–Co electrocatalyst for selective oxygen reduction to use in implantable glucose fuel cell

In this research, the activity of Fe–Co/KB (ketjenblack carbon) has been studied as a cathode catalyst for oxygen reduction reaction (ORR) in phosphate buffer saline (PBS) in presence of a solution containing low concentrations of glucose and amino acids mixture (near to physiological tissue fluid in the human body). It is worthwhile to mention that Fe–Co/KB cathode catalyst with size of 3 nm, determined by TEM, indicated an exceptional selectivity towards ORR. Results also revealed that Fe–Co/KB has a higher activity compare to 80%wt Pt/C in ORR with a superior tolerance towards poisoning agents.Further electrochemical investigations were carried out in a two-chamber implantable glucose fuel cell (IGFC) utilizing Fe–Co/KB in the cathode side. Time-dependent evaluation of cell voltage at constant current discharge 0.02 mAcm⁻² in PBS (pH = 7.4) solution containing 5 mM glucose showed only 16% loss in cathode potential; demonstrating an acceptable performance of cathode catalyst in IGFC.     

Ag nanoparticles on mesoporous carbon support as cathode catalyst for anion exchange membrane fuel cell

Silver nanocatalyst (40 wt%) is deposited on commercial mesoporous carbon support material (Ag/C) using two different wet chemical methods, to obtain high electrochemically active surface area. The catalyst materials are characterized by scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, thermogravimetric analysis and are evaluated toward the oxygen reduction reaction (ORR) in alkaline media employing the rotating disk electrode method. It is worth noting that the Ag/C leads to oxygen reduction through a direct four-electron pathway in alkaline medium. The silver catalyst on mesoporous carbon exhibits relatively higher mass activity for ORR (38 A g⁻¹) compared to that with Vulcan carbon (32 A g⁻¹) at −0.2 V vs SCE at room temperature. Anion exchange membrane fuel cell shows maximum power density of 310 mW cm⁻² with Ag/C cathode catalyst using H₂ and O₂ gases at 65% RH conditions at 65 °C.     

Electrochemical performances of LiNiCoMn bifunctional electrode for low temperature solid oxide fuel cells

Lithium transition metal oxides LiNi_0.83Co_0.11Mn_0.06O₂ (NCM-83) and LiNi_0.8Co_0.1Mn_0.1O₂ (NCM-811) are prepared and acted as cathodes and bifunctional electrodes for low temperature solid oxide fuel cells with H₂ and CH₄ fuels. The Ni anode-supported cell with NCM-83 cathode exhibits maximum power density (P_max) of 0.72 W cm⁻² with H₂ fuel at 600 °C. The symmetric cell with NCM-83 electrodes shows high P_max of 0.465 W cm⁻² with H₂ fuel and 0.354 W cm⁻² with CH₄ fuel at 600 °C. And the P_max of the cell with NCM-811 as anode and NCM-83 as cathode is 0.204W cm⁻² with H₂ fuel at 600 °C. The oxygen vacancies in NCM materials are conducive to the rapid oxygen ion conduction of the cathode, and in the anodic reduction atmosphere, the NCM materials will generate Ni/Co active particles in situ, proving the NCM materials can be advanced bifunctional electrode materials for hydrogen oxidation reaction and oxygen reduction reaction at low temperature.     

Biomass-derived N-doped porous activated carbon as a high-performance and cost-effective pH-universal oxygen reduction catalyst in fuel cell

Nitrogen (N) doped porous activated carbons (TGC-T) derived from tofu gel are prepared through a facile, economic and eco-friendly method. The as-prepared TGC-900 possesses high specific surface area (651.78 m² g⁻¹) and homogeneous doping N (Content of N: 5.52 at.%). Reasonably, TGC-900 exhibits excellent oxygen reduction reaction (ORR) activity, stability and methanol resistance in neutral, alkaline and acidic medium. Moreover, TGC-900 also shows outstanding ORR performance in the application of microbial fuel cell (MFC) with the highest output voltage (544 ± 6 mV) and maximum power density (977 ± 32 mW m⁻²). Inspiringly, four single-chamber air cathode MFCs (AC-MFCs) in series can drive a light-emitting diode (LED) to work is firstly reported which further provides a more intuitively method to evaluate the performance of generating electricity for MFCs. Thus, the high performance and cost-effective ORR catalyst TGC-900 is expected to apply in the field of fuel cells.     

Iron and cobalt containing electrospun carbon nanofibre-based cathode catalysts for anion exchange membrane fuel cell

The use of Pt-based cathode catalyst materials hinders the widespread application of anion exchange membrane fuel cells (AEMFCs). Herein, we present a non-precious metal catalyst (NPMC) material based on pyrolysed Fe and Co co-doped electrospun carbon nanofibres (CNFs). The prepared materials are studied as oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysts in alkaline and acidic environments. High activity towards the ORR in alkaline solution indicated the suitability of the prepared NPMCs for the application at the AEMFC cathode. In the AEMFC test, the membrane-electrode assembly bearing a cathode with the nanofibre-based catalyst prepared with the ionic liquid (IL) (Fe/Co/IL–CNF–800b) showed the maximum power density (P_max) of 195 mW cm⁻², which is 78% of the P_max obtained with a commercial Pt/C cathode catalyst. Such high ORR electrocatalytic activity was attributed to the unique CNF structure, high micro-mesoporosity, different nature of nitrogen species and metal-N_x active centres.     

Carbon supported Pt–Co (3:1) alloy as improved cathode electrocatalyst for direct ethanol fuel cells

In direct alcohol fuel cells, ethanol crossover causes a less serious effect compared to that of methanol because of both its smaller permeability through the Nafion^® membrane and its slower electrochemical oxidation kinetics on a Pt/C cathode. The main interest in direct ethanol fuel cells (DEFCs) is to find an anode catalyst with high activity for the oxidation of ethanol. However, due to the low activity of pure platinum for the oxygen reduction reaction (ORR), research on cathode electrocatalysts with improved ORR and the same or improved ethanol tolerance than that of Pt are also in progress. In this work, a commercial carbon supported Pt–Co (3:1) electrocatalyst (E-TEK) was investigated as cathode material in DEFCs and the activity compared to that of Pt. In the cathodic potential region (0.7–0.9 V versus RHE) Pt/C and Pt–Co/C showed the same activity for the oxidation of crossover ethanol. But the performance of Pt–Co/C as cathode material in DEFCs in the temperature range 60–100 °C is better than that of Pt/C both in terms of mass activity and specific activity, due to an improved activity of the alloy for oxygen reduction.     

Advanced electrocatalytic activity of praseodymium-deficient copper-based oxygen electrodes for solid oxide fuel cells

Herein praseodymium-deficient Pr_1.90−xCe_0.1CuO₄ oxides are evaluated as potential oxygen electrodes for solid oxide fuel cells (SOFCs). Introducing Pr-deficiency promotes the oxygen vacancy concentration, further improving electrocatalytic activity of the Pr_1.90−xCe_0.1CuO₄ electrodes towards oxygen reduction reaction (ORR). The Pr_1.75Ce_0·.1CuO₄ (P_1·75CC) component exhibits outstanding electrode performance, as supported by a polarization resistance as low as 0.025 Ω cm² and high peak power density of the single cell (1.11 W cm⁻²) at 700 °C. In addition, the rate-limiting steps for ORR kinetics are determined to be the charge transfer reaction and oxygen adsorption/diffusion process on the electrode surface. This work highlights an effective way for developing the cathode candidates with high electrocatalytic activity and superior stability.     

Performance of an alkaline direct ethanol fuel cell with hydrogen peroxide as oxidant

An alkaline direct ethanol fuel cell (DEFC) with hydrogen peroxide as the oxidant is developed and tested. The present fuel cell consists of a non-platinum anode, an anion exchange membrane, and a non-platinum cathode. It is demonstrated that the peak power density of the fuel cell is 130 mW cm⁻² at 60 °C (160 mW cm⁻² at 80 °C), which is 44% higher than that of the same fuel cell setup but with oxygen as the oxidant. The improved performance as compared with the fuel cell with oxygen as the oxidant is mainly attributed to the superior electrochemical kinetics of the hydrogen peroxide reduction reaction and the reduced ohmic loss associated with the liquid oxidant.     

An oxygen reduction reaction active and durable SOFC cathode/electrolyte interface achieved via a cost-effective spray-coating

One of the critical obstacles for commercialization of solid oxide fuel cells (SOFCs) technology is to develop efficient interfaces between cathode and electrolyte that enable high activity toward oxygen reduction reaction (ORR) while maintain long-term durability. Here, we report a cost-effective spray-coating process that applied in the building of an ORR active and durable cathode/electrolyte interface. When tested at 750 °C, such spray-coated cathodes show a typical interfacial polarization resistance of ~0.059 Ωcm², much lower than that of ~0.10 Ωcm² for screen-printed cathodes. Detailed distribution of relaxation time analyses of the impedance spectra over time indicates that the capability of mass transfer and surface exchange process in the spray-coated cathode/electrolyte interface has been enhanced and maintained in the testing periods of ~100 h. As a result, a Ni-based anode supported cell with thin electrolyte and spray-coated cathodes shows an excellent peak power density of 1.012 Wcm⁻², much higher than that of 0.712 Wcm⁻² for cells with screen-printed cathodes, when tested at 750 °C using wet H₂ as fuel and ambient air as oxidant. It is demonstrated that ORR activity and durability of the SOFC cathodes can be dramatically enhanced via a cost-effective spray-coating process.     

Comparative study between platinum supported on carbon and non-noble metal cathode catalyst in alkaline direct ethanol fuel cell (ADEFC)

In this study, we reported a comparison study between the performance of the commercial non-noble metal cathode electrode (made by Hypermec™ K14 catalyst - provided by Acta S.p.A.) and cathode electrode containing 10 wt% Pt/C, in the alkaline direct ethanol fuel cell (ADEFC) under different conditions.Further electrochemical investigations have been done by RDE and driven mode cell to compare the intrinsic activity and selectivity of 10 wt% Pt/C and Hypermec™ K14 transition metals cathode catalysts. It is worthwhile to point out that Hypermec™ K14 cathode catalyst shows a remarkable selectivity to oxygen reduction and it has a superior intrinsic activity in oxygen reduction reaction (ORR) especially in terms of volumetric current density (A/cm³). Test results of active DEFC made by non-noble cathode catalyst showed superior performance compared to the cell made by 10 wt% Pt/C cathode catalysts in terms of power density and OCV at 60 °C and ambient pressure. This result is related to the higher ORR kinetic of non-noble metal cathode catalyst in alkaline media.     

Application of synthesized porous graphitic carbon nitride and it's composite as excellent electrocatalysts in microbial fuel cell

The performance of microbial fuel cells (MFCs) consisting of exfoliated porous graphitic carbon nitride (ep-GCN) and its composite with acetylene black (AB) as cathode catalyst is evaluated. The cyclic voltammetry and electrochemical impedance spectroscopy of composite ep-GCN-AB indicated excellent oxygen reduction reaction activity and comparable charge transfer resistance with respect to Pt–C. The absence of X-ray diffraction peak at 2θ = 13° (corresponding to stacked structure of bulk GCN) indicated reduction in thickness. Four MFCs were operated with simulated wastewater with chemical oxygen demand (COD) of 3000 mg L⁻¹. The maximum power densities of MFC-GAB (14.74 ± 0.17 W m⁻³), MFC-PAB (15.68 ± 0.58 W m⁻³) and MFC-G (12.47 ± 0.30 W m⁻³) using ep-GCN-AB, Pt–C and ep-GCN electrocatalyst, respectively, were 2.6, 2.7 and 2.2 times higher than MFC-AB operated with only acetylene black coated cathode. The investigation demonstrates that ep-GCN and its composites can be utilized as excellent cathode catalysts in MFCs at 20 folds lesser cost than Pt–C.     

Biomass pectin-derived N,S-enriched carbon with hierarchical porous structure as a metal-free catalyst for enhancing bio-electricity generation

Heteroatoms-doped carbon-based materials (with non-precious metals or no metals) with porous structure have already shown high catalytic activities for oxygen reduction reaction (ORR), especially in microbial fuel cells (MFCs). Here, we use pectin extracted from pomelo peels as carbon source to prepare metal-free and sulphur/nitrogen co-doped partially-graphitized carbon (HP-SN-PGCs) by using silica nanospheres as sacrificial templates. Single-chamber MFC (SC-MFC) with HP-SN-PGC-0.5 (0.5 g of silica) cathode has the shortest start-up time (45 h) and lowest charge transfer resistance (19.3 Ω). The maximum power density of HP-SN-PGC-0.5 (1161.34 mW m⁻²) cathode is higher than that of Pt/C (1116.90 mW m⁻²) at the initial cycle. After 75 d operation, power density of HP-SN-PGC-0.5 cathode only declines 4.6%, which is more stable than that of Pt/C (37.69%). HP-SN-PGC-0.5 has a highly porous structure (869.25 m² g⁻¹) by removal of templates and Fe species (as the graphitization catalyst) to facilitate exposure of active sites and diffusion of ORR-related intermediates (OH⁻ and HO₂⁻, etc) to accessible active sites. N and S species provide highly active sites to enhance OH⁻ generation to conduct the 4e⁻ ORR process. Thus, this study presents a viable ORR catalyst with high activity and long-term stability for bio-electricity generation from organic wastewater in SC-MFCs.     

Electrochemical study of lithiated transition metal oxide composite as symmetrical electrode for low temperature ceramic fuel cells

In this work, Lithiated NiCuZnO_x (LNCZO) composite is synthesized and evaluated as a potential symmetrical electrode for ceria-carbonate composite electrolyte based low temperature ceramic fuel cells. Its crystal structures, the hydrogen oxidation/oxygen reduction electrochemical activities and fuel cell performances are systematically examined on the symmetrical cell configuration. Nano crystallite particles in the form of composite are observed for these oxides. The LNCZO shows relatively high catalytic activities for hydrogen oxidation and oxygen reduction reaction according to the electrochemical impedance spectroscopy measurements. A remarkable low oxygen reduction activation energy of 42 kJ mol⁻¹ is obtained on the LNCZO/ceria-carbonate composite, demonstrating excellent electro-catalytic activity. Especially, the catalytic activity can be further improved in the presence of water in the cathode chamber. The results show that the lithiated transition metal oxide composite is a promising symmetrical electrode for ceria-carbonate electrolyte and composite approach might a probable solution to develop super-performance electrodes for reduced temperature ceramic fuel cells.     

Carbon supported Ag nanoparticles with different particle size as cathode catalysts for anion exchange membrane direct glycerol fuel cells

The effect of Ag particle size on oxygen reduction reaction (ORR) at the cathode was investigated in anion exchange membrane direct glycerol fuel cells (AEM-DGFC) with oxygen as an oxidant. At the anode, high purity glycerol (99.8 wt%) or crude glycerol (88 wt%, from soybean biodiesel) was used as fuel, and commercial Pt/C served as the anode catalyst. A solution phase-based nanocapsule synthesis method was successfully developed to prepare the non-precious Ag/C cathode catalyst, with LiBEt₃H as a reducing agent. XRD and TEM characterizations show that as-synthesized Ag nanoparticles (NP) with a size of 2–9 nm are well dispersed on the Vulcan XC-72 carbon black support. Commercial Ag nanoparticles with a size of 20–40 nm were also supported on carbon black as a control sample. The results show that higher peak power density was obtained in AEM-DGFC employing an Ag-NP catalyst with smaller particle size: nanocapsule made Ag-NP > commercial Ag-NP (Alfa Aesar, 99.9%). With the nanocapsule Ag-NP cathode catalyst, the peak power density and open circuit voltage (OCV) of AEM-DGFC with high-purity glycerol at 80 °C are 86 mW cm⁻² and 0.73 V, respectively. These are much higher than 45 mW cm⁻² and 0.68 V for the AEM-DGFC with the commercial Ag/C cathode catalyst, which can be attributed to the enhanced kinetics and reduced internal resistance. Directly fed with crude glycerol, the AEM-DGFC with the nanocapsule Ag-NP cathode catalyst shows an encouraging peak power density of 66 mW cm⁻², which shows great potential of direct use of biodiesel waste fuel for electricity generation.     

Hybrid palladium-ceria nanorod electrocatalysts applications in oxygen reduction and ethanol oxidation reactions in alkaline media

Fossil fuel alternatives are being increasingly studied, and alkaline direct ethanol fuel cells (ADEFC) have acquired importance, as to ethanol is a renewable fuel. In this context, the aims of the present study were to synthesize, characterize and evaluate electrocatalytic activity in oxygen reduction reaction (ORR) and ethanol oxidation reaction (EOR) using hybrid electrocatalysts based on Pd nanoparticles and CeO₂ nanorods supported on carbon black for application in ADEFC. The highest OCV, maximum current and power densities obtained using Pd₁₅(CeO₂ NR)₁₀(Vn)₇₅ as the cathode and Pd₁₀(CeO₂ NR)₂₀(Vn)₇₀ as the anode were 1270 mV, 190 mA cm^?2 and 65 mW cm^?2, respectively. These interesting results are justified by the highest I_D/I_G ratio and ECSA, which suggest a high number of oxygenated species, defects and vacancies in these electrocatalysts and by the synergistic effect between CeO₂ NR and Pd nanoparticles. Therefore, these hybrid electrocatalysts are promising for ADEFC applications.     

Low thermal expansion material Bi0·5Ba0·5FeO3-δ in application for proton-conducting ceramic fuel cells cathode

The cobalt-free material of Bi³⁺-doped BaFeO_3-δ (BBFO) is synthesized and applied as a cathode material for intermediate-temperature solid oxide fuel cells (IT-SOFCs) with proton conducting electrolyte Ba(Zr_0·1Ce_0·7Y_0.2)O₃ (BZCY). The as-prepared BBFO demonstrates a tetragonal structure with sufficient chemical compatibility, high thermal stability and low thermal expansion coefficient. BBFO exhibits higher electrical conductivity of 4.1 S cm⁻¹compared to the parent material BaFeO_3-δ (BFO) of 3.5 S cm⁻¹. The composite cathode BBFO-BZCY with the mass ratio of 7:3 presents a relatively low R_p of 0.128 Ω cm² at 700 °C in air. According to the oxygen reduction reaction process, the rate-determining step is transformed from charge transfer to oxygen gas (O₂) adsorption-dissociation with the rising temperature. In addition, the performance of the anode-supported cell NiO-BZCY∣BZCY∣BBFO-BZCY is 120 mW cm⁻² as the thickness of electrolyte is 150 μm. It thus promises BBFO as a novel cathode for proton-conducting ceramic fuel cells.