Influence of platinum group metal-free catalyst synthesis on microbial fuel cell performance

Giving New Life to Waste Cigarette Butts: Transformation into Platinum Group Metal-Free Electrocatalysts for Oxygen Reduction Reaction in Acid, Neutral and Alkaline Environment

Following the core theme of a circular economy, a novel strategy to upcycle cigarette butt waste into platinum group metal (PGM)-free metal nitrogen carbon (M-N-C) electrocatalysts for oxygen reduction reaction (ORR) is presented. The experimental route was composed of (i) the transformation of the powdered cigarette butts into carbonaceous char via pyrolysis at 450 °C, 600 °C, 750 °C and 900 °C, (ii) the porosity activation with KOH and (iii) the functionalization of the activated chars with iron (II) phthalocyanine (FePc). The electrochemical outcomes obtained by the rotating disk electrode (RRDE) technique revealed that the sample pyrolyzed at 450 °C (i.e., cig_450) outperformed the other counterparts with its highest onset (Eon) and half-wave potentials (E1/2) and demonstrated nearly tetra-electronic ORR in acidic, neutral and alkaline electrolytes, all resulting from the optimal surface chemistry and textural properties.

Degradation of β-lactam antibiotic ampicillin using sustainable microbial peroxide producing cell system

The enormous use of synthetic antibiotic and personal care products has impacted the natural microbiome and ecosystem. Overtime, treatment technologies developed suffered due to incomplete removal hence, a pilot dual-chambered microbial peroxide-producing cell that degrades ampicillin catalyzed by homogenous Fenton-reaction was designed. The system reported maximum current at 16.714 ± 0.048 µAcm^-2, power output of 1.956 ± 0.015 mW m^-2; 88 ± 2.90 mM of H₂O₂ generation with Na₂SO₄ that degraded 95.9 ± 3.00 to 97.8 ± 3.20% of 10 mg L^-1ampicillin within 72 hrs with electro-active Shewanella putrefaciens. An E. coli bioactivity assay with ampicillin exhibited no sensitivity zone due to the loss of activity. Analytical spectroscopic studies reveal β-Lactam ring deformation; Liquid Chromatography-Mass Spectroscopy clearly shows the presence of degradation metabolites. A sustainable wastewater treatment with 72 ± 4.5% reduction in anodic chemical oxygen demand was achieved. Present results designate the technology, as promising for effective antibiotics removal for wastewater treatment concomitant with electricity generation.

Waste Face Surgical Mask Transformation into Crude Oil and Nanostructured Electrocatalysts for Fuel Cells and Electrolyzers

A novel route for the valorization of waste into valuable products was developed. Surgical masks commonly used for COVID 19 protection by stopping aerosol and droplets have been widely used, and their disposal is critical and often not properly pursued. This work intended to transform surgical masks into platinum group metal-free electrocatalysts for oxygen reduction reaction (ORR) and hydrogen evolution reaction (HER) as well as into crude oil. Surgical masks were subjected to controlled-temperature and -atmosphere pyrolysis, and the produced char was then converted into electrocatalysts by functionalizing it with metal phthalocyanine of interest. The electrocatalytic performance characterization towards ORR and HER was carried out highlighting promising activity. At different temperatures, condensable oil fractions were acquired and thoroughly analyzed. Transformation of waste surgical masks into electrocatalysts and crude oil can open new routes for the conversion of waste into valuable products within the core of the circular economy.

Activated carbon supported Fe–Cu–NC as an efficient cathode catalyst for a microbial fuel cell

Herein, the output power density produced by Fe–Cu–NC-x as the cathode catalyst of a MFC was higher than that of the AC control.

Recent Advances in Waste Plastic Transformation into Valuable Platinum-Group Metal-Free Electrocatalysts for Oxygen Reduction Reaction

Plastic waste causes severe environmental hazards, owing to inadequate disposal and limited recycling. Under the framework of circular economy, there are urgent demands to valorize plastic waste more safely and sustainably. Therefore, much scientific interest has been witnessed recently in plastic waste-derived electrocatalysts for the oxygen reduction reaction (ORR), where the plastic waste acts as a cost-effective and easily available precursor for the carbon backbone. The ORR is not only a key efficiency indicator for fuel cells and metal-air batteries but also a major obstacle for their commercial realization. The applicability of the aforementioned electrochemical devices is limited, owing to sluggish ORR activity and expensive platinum-group metal electrocatalysts. However, waste-derived ORR electrocatalysts are emerging as a potential substitute that could be inexpensively fabricated upon the conversion of plastic waste into active materials containing earth-abundant transition metals. In this Minireview, very recent research developments regarding plastic waste-derived ORR electrocatalysts are critically summarized with a prime focus on the followed synthesis routes, physicochemical properties of the derived electrocatalysts, and their ultimate electrochemical performance. Finally, the prospects for the future development of plastic waste-derived electrocatalysts are discussed.

How Comparable are Microbial Electrochemical Systems around the Globe? An Electrochemical and Microbiological Cross-Laboratory Study

A cross-laboratory study on microbial fuel cells (MFC) which involved different institutions around the world is presented. The study aims to assess the development of autochthone microbial pools enriched from domestic wastewater, cultivated in identical single-chamber MFCs, operated in the same way, thereby approaching the idea of developing common standards for MFCs. The MFCs are inoculated with domestic wastewater in different geographic locations. The acclimation stage and, consequently, the startup time are longer or shorter depending on the inoculum, but all MFCs reach similar maximum power outputs (55±22 μW cm-2 ) and COD removal efficiencies (87±9 %), despite the diversity of the bacterial communities. It is inferred that the MFC performance starts when the syntrophic interaction of fermentative and electrogenic bacteria stabilizes under anaerobic conditions at the anode. The generated power is mostly limited by electrolytic conductivity, electrode overpotentials, and an unbalanced external resistance. The enriched microbial consortia, although composed of different bacterial groups, share similar functions both on the anode and the cathode of the different MFCs, resulting in similar electrochemical output.

Ti3C2 supported transition metal oxides and silver as catalysts toward efficient electricity generation in microbial fuel cells

The improved electricity generation performance of MFCs could be attributed to the Ti₃C₂ support and the synergistic effect between transition metal oxides and silver for ORR.

Air-breathing cathode self-powered supercapacitive microbial fuel cell with human urine as electrolyte

In this work, a membraneless microbial fuel cell (MFC) with an empty volume of 1.5 mL, fed continuously with hydrolysed urine, was tested in supercapacitive mode (SC-MFC). In order to enhance the power output, a double strategy was used: i) a double cathode was added leading to a decrease in the equivalent series resistance (ESR); ii) the apparent capacitance was boosted up by adding capacitive features on the anode electrode. Galvanostatic (GLV) discharges were performed at different discharge currents. The results showed that both strategies were successful obtaining a maximum power output of 1.59 ± 0.01 mW (1.06 ± 0.01 mW mL⁻¹) at pulse time of 0.01 s and 0.57 ± 0.01 mW (0.38 ± 0.01 mW mL⁻¹) at pulse time of 2 s. The highest energy delivered at i_pulse equal to 2 mA was 3.3 ± 0.1 mJ. The best performing SC-MFCs were then connected in series and parallel and tested through GLV discharges. As the power output was similar, the connection in parallel allowed to roughly doubling the current produced. Durability tests over ≈5.6 days showed certain stability despite a light overall decrease.

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Air-breathing microbial fuel cell was tested in supercapacitive mode.

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A double cathode addition lead to a decrease in ohmic resistance.

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Apparent capacitance was boosted up by adding capacitive features.

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Maximum power output of 1.59 mW (1.06 mW mL⁻¹) was reached at t_pulse 0.01s.

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Series and parallel connections improved the galvanostatic discharges.

Platinum Group Metal-Free Catalysts for Oxygen Reduction Reaction: Applications in Microbial Fuel Cells

Scientific and technological innovation is increasingly playing a role for promoting the transition towards a circular economy and sustainable development. Thanks to its dual function of harvesting energy from waste and cleaning up waste from organic pollutants, microbial fuel cells (MFCs) provide a revolutionary answer to the global environmental challenges. Yet, one key factor that limits the implementation of larger scale MFCs is the high cost and low durability of current electrode materials, owing to the use of platinum at the cathode side. To address this issue, the scientific community has devoted its research efforts for identifying innovative and low cost materials and components to assemble lab-scale MFC prototypes, fed with wastewaters of different nature. This review work summarizes the state-of the-art of developing platinum group metal-free (PGM-free) catalysts for applications at the cathode side of MFCs. We address how different catalyst families boost oxygen reduction reaction (ORR) in neutral pH, as result of an interplay between surface chemistry and morphology on the efficiency of ORR active sites. We particularly review the properties, performance, and applicability of metal-free carbon-based materials, molecular catalysts based on metal macrocycles supported on carbon nanostructures, M-N-C catalysts activated via pyrolysis, metal oxide-based catalysts, and enzyme catalysts. We finally discuss recent progress on MFC cathode design, providing a guidance for improving cathode activity and stability under MFC operating conditions.

Supercapacitive paper based microbial fuel cell: High current/power production within a low cost design

Microbial fuel cells (MFCs) with paper separators and liquid containing elements were investigated in supercapacitive mode. MFCs (15 mL) in a supercapacitive configuration, consisted of plain wrapped carbon veil anode (negative) and conductive latex cathode (positive). The internal supercapacitor is discharged galvanostatically and is self-recharged as red-ox reactions occur on both electrodes. MFCs were discharged at different current pulses varying from 1 mA to 7 mA. The MFCs had an equivalent series resistance of 41.2 ± 3.5 Ω caused mainly by the cathode. A maximum power of 1.380 ± 0.083 mW (0.092 ± 0.006 mW mL⁻¹) was measured. Durability tests were conducted over 24 h collecting 1000 discharge cycles (0.5 s) and self-recharges (85 s) at a current of 1 mA. Over time the anode potential dropped causing a decline in performance perhaps due to evaporation of liquid from the pyramidal structure. Resistance and apparent capacitance measured during the durability test remained approximately constant during the cycles.

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Supercapacitor paper-based MFCs are reported for the first time.

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Galvanostatic discharges at different current pulses (1 mA to 7 mA) were analysed.

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Equivalent series resistance (ESR) and apparent capacitance (C) were identified.

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Maximum power achieved was 1.380 ± 0.083 mW (0.092 ± 0.006 mW mL⁻¹).

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The system stability was investigated through 1000 discharge/self-recharge cycles.

Multi-functional microbial fuel cells for power, treatment and electro-osmotic purification of urine

BACKGROUND

In this work, a small-scale ceramic microbial fuel cell (MFC) with a novel type of metal-carbon-derived electrocatalyst containing iron and nicarbazin (Fe-NCB) was developed, to enhance electricity generation from neat human urine. Substrate oxidation at the anode provides energy for the separation of ions and recovery from urine without any chemical or external power additions.

RESULTS

The catalyst was shown to be effective in clear electrolyte synthesis of high pH, compared with a range of carbon-based metal-free materials. Polarisation curves of tested MFCs showed up to 53% improvement (44.8 W m^-3) in performance with the use of Fe-NCB catalyst.Catholyte production rate and pH directly increased with power performance while the conductivity decreased showing visually clear extracted liquid in the best-performing MFCs.

CONCLUSIONS

Iron based catalyst Fe-NCB was shown to be a suitable electrocatalyst for the air-breathing cathode, improving power production from urine-fed MFCs. The results suggest electrochemical treatment through electro-osmotic drag while the electricity is produced and not consumed. Electro-osmotic production of clear catholyte is shown to extract water from urine against osmotic pressure. Recovering valuable resources from urine would help to transform energy intensive treatments to resource production, and will create opportunities for new technology development. © 2018 The Authors. Journal of Chemical Technology & Biotechnology published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Iron-streptomycin derived catalyst for efficient oxygen reduction reaction in ceramic microbial fuel cells operating with urine

In recent years, the microbial fuel cell (MFC) technology has drawn the attention of the scientific community due to its ability to produce clean energy and treat different types of waste at the same time. Often, expensive catalysts are required to facilitate the oxygen reduction reaction (ORR) and this hinders their large-scale commercialisation. In this work, a novel iron-based catalyst (Fe-STR) synthesised from iron salt and streptomycin as a nitrogen-rich organic precursor was chemically, morphologically and electrochemically studied. The kinetics of Fe-STR with and without being doped with carbon nanotubes (CNT) was initially screened through rotating disk electrode (RDE) analysis. Then, the catalysts were integrated into air-breathing cathodes and placed into ceramic-type MFCs continuously fed with human urine. The half-wave potential showed the following trend Fe-STR > Fe-STR-CNT ≫ AC, indicating better kinetics towards ORR in the case of Fe-STR. In terms of MFC performance, the results showed that cathodes containing Fe-based catalyst outperformed AC-based cathodes after 3 months of operation. The long-term test reported that Fe-STR-based cathodes allow MFCs to reach a stable power output of 104.5 ± 0.0 μW cm-2, 74% higher than AC-based cathodes (60.4 ± 3.9 μW cm-2). To the best of the Authors' knowledge, this power performance is the highest recorded from ceramic-type MFCs fed with human urine.

Self-stratified and self-powered micro-supercapacitor integrated into a microbial fuel cell operating in human urine

A self-stratified microbial fuel cell fed with human urine with a total internal volume of 0.55 ml was investigated as an internal supercapacitor, for the first time. The internal self-stratification allowed the development of two zones within the cell volume. The oxidation reaction occurred on the bottom electrode (anode) and the reduction reaction on the top electrode (cathode). The electrodes were discharged galvanostatically at different currents and the two electrodes were able to recover their initial voltage value due to their red-ox reactions. Anode and cathode apparent capacitance was increased after introducing high surface area activated carbon embedded within the electrodes. Peak power produced was 1.20 ± 0.04 mW (2.19 ± 0.06 mW ml-1) for a pulse time of 0.01 s that decreased to 0.65 ± 0.02 mW (1.18 ± 0.04 mW ml-1) for longer pulse periods (5 s). Durability tests were conducted over 44 h with ≈2600 discharge/recharge cycles. In this relatively long-term test, the equivalent series resistance increased only by 10% and the apparent capacitance decreased by 18%.

Increased power generation in supercapacitive microbial fuel cell stack using Fe-N-C cathode catalyst

The anode and cathode electrodes of a microbial fuel cell (MFC) stack, composed of 28 single MFCs, were used as the negative and positive electrodes, respectively of an internal self-charged supercapacitor. Particularly, carbon veil was used as the negative electrode and activated carbon with a Fe-based catalyst as the positive electrode. The red-ox reactions on the anode and cathode, self-charged these electrodes creating an internal electrochemical double layer capacitor. Galvanostatic discharges were performed at different current and time pulses. Supercapacitive-MFC (SC-MFC) was also tested at four different solution conductivities. SC-MFC had an equivalent series resistance (ESR) decreasing from 6.00 Ω to 3.42 Ω in four solutions with conductivity between 2.5 mScm^-1 and 40 mScm^-1. The ohmic resistance of the positive electrode corresponded to 75-80% of the overall ESR. The highest performance was achieved with a solution conductivity of 40 mS cm^-1 and this was due to the positive electrode potential enhancement for the utilization of Fe-based catalysts. Maximum power was 36.9 mW (36.9 W m^-3) that decreased with increasing pulse time. SC-MFC was subjected to 4520 cycles (8 days) with a pulse time of 5 s (i_pulse 55 mA) and a self-recharging time of 150 s showing robust reproducibility.

Multi-walled carbon nanotube and carbide-derived carbon supported metal phthalocyanines as cathode catalysts for microbial fuel cell applications

Metal phthalocyanine (CoPc and FePc) modified MWCNT or CDC materials were explored as superior cathode catalysts for MFC technology.

Oxygen Reduction Reaction Electrocatalysts Derived from Iron Salt and Benzimidazole and Aminobenzimidazole Precursors and Their Application in Microbial Fuel Cell Cathodes

In this work, benzimidazole (BZIM) and aminobenzimidazole (ABZIM) were used as organic-rich in nitrogen precursors during the synthesis of iron-nitrogen-carbon (Fe-N-C) based catalysts by sacrificial support method (SSM) technique. The catalysts obtained, denoted Fe-ABZIM and Fe-BZIM, were characterized morphologically and chemically through SEM, TEM, and XPS. Moreover, these catalysts were initially tested in rotating ring disk electrode (RRDE) configuration, resulting in similar high electrocatalytic activity toward oxygen reduction reaction (ORR) having low hydrogen peroxide generated (<3%). The ORR performance was significantly higher compared to activated carbon (AC) that was the control. The catalysts were then integrated into air-breathing (AB) and gas diffusion layer (GDL) cathode electrode and tested in operating microbial fuel cells (MFCs). The presence of Fe-N-C catalysts boosted the power output compared to AC cathode MFC. The AB-type cathode outperformed the GDL type cathode probably because of reduced catalyst layer flooding. The highest performance obtained in this work was 162 ± 3 μWcm^-2. Fe-ABZIM and Fe-BZIM had similar performance when incorporated to the same type of cathode configuration. Long-term operations show a decrease up to 50% of the performance in two months operations. Despite the power output decrease, the Fe-BZIM/Fe-ABZIM catalysts gave a significant advantage in fuel cell performance compared to the bare AC.

Iron-Nicarbazin derived platinum group metal-free electrocatalyst in scalable-size air-breathing cathodes for microbial fuel cells

In this work, a platinum group metal-free (PGM-free) catalyst based on iron as transitional metal and Nicarbazin (NCB) as low cost organic precursor was synthesized using Sacrificial Support Method (SSM). The catalyst was then incorporated into a large area air-breathing cathode fabricated by pressing with a large diameter pellet die. The electrochemical tests in abiotic conditions revealed that after a couple of weeks of successful operation, the electrode experienced drop in performances in reason of electrolyte leakage, which was not an issue with the smaller electrodes. A decrease in the hydrophobic properties over time and a consequent cathode flooding was suspected to be the cause. On the other side, in the present work, for the first time, it was demonstrated the proof of principle and provided initial guidance for manufacturing MFC electrodes with large geometric areas. The tests in MFCs showed a maximum power density of 1.85 W m^-2. The MFCs performances due to the addition of Fe-NCB were much higher compared to the iron-free material. A numerical model using Nernst-Monod and Butler-Volmer equations were used to predict the effect of electrolyte solution conductivity and distance anode-cathode on the overall MFC power output. Considering the existing conditions, the higher overall power predicted was 3.6 mW at 22.2 S m^-1 and at inter-electrode distance of 1 cm.

Enhancement of microbial fuel cell performance by introducing a nano-composite cathode catalyst

Iron aminoantipyrine (Fe-AAPyr), graphene nanosheets (GNSs) derived catalysts and their physical mixture Fe-AAPyr-GNS were synthesized and investigated as cathode catalysts for oxygen reduction reaction (ORR) with the activated carbon (AC) as a baseline. Fe-AAPyr catalyst was prepared by Sacrificial Support Method (SSM) with silica as a template and aminoantipyrine (AAPyr) as the organic precursor. 3D-GNS was prepared using modified Hummers method technique. The Oxygen Reduction Reaction (ORR) activity of these catalysts at different loadings was investigated by using rotating ring disk (RRDE) electrode setup in the neutral electrolyte. The performance of the catalysts integrated into air-breathing cathode was also investigated. The co-presence of GNS (2 mg cm⁻²) and Fe-AAPyr (2 mg cm⁻²) catalyst within the air-breathing cathode resulted in the higher power generation recorded in MFC of 235 ± 1 μW cm⁻². Fe-AAPyr catalyst itself showed high performance (217 ± 1 μW cm⁻²), higher compared to GNS (150 ± 5 μW cm⁻²) while AC generated power of roughly 104 μW cm⁻².

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Fe-AAPyr and GNS were synthesized and characterized.

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Rotating ring disk electrode (RRDE) setup was performed in the neutral electrolyte.

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Fe-AAPyr had higher half wave potential and lower H₂O₂ production.

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The combination of Fe-AAPyr and GNS led to a power generation of 235 ± 1 μWcm⁻².

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Both Fe-AAPyr and GNS outperformed compared to activated carbon control.

Power generation in microbial fuel cells using platinum group metal-free cathode catalyst: Effect of the catalyst loading on performance and costs

Platinum group metal-free (PGM-free) catalyst with different loadings was investigated in air breathing electrodes microbial fuel cells (MFCs). Firstly, the electrocatalytic activity towards oxygen reduction reaction (ORR) of the catalyst was investigated by rotating ring disk electrode (RRDE) setup with different catalyst loadings. The results showed that higher loading led to an increased in the half wave potential and the limiting current and to a further decrease in the peroxide production. The electrons transferred also slightly increased with the catalyst loading up to the value of ≈3.75. This variation probably indicates that the catalyst investigated follow a 2x2e- transfer mechanism. The catalyst was integrated within activated carbon pellet-like air-breathing cathode in eight different loadings varying between 0.1 mgcm-2 and 10 mgcm-2. Performance were enhanced gradually with the increase in catalyst content. Power densities varied between 90 ± 9 μWcm-2 and 262 ± 4 μWcm-2 with catalyst loading of 0.1 mgcm-2 and 10 mgcm-2 respectively. Cost assessments related to the catalyst performance are presented. An increase in catalyst utilization led to an increase in power generated with a substantial increase in the whole costs. Also a decrease in performance due to cathode/catalyst deterioration over time led to a further increase in the costs.