Application Of Microbial Electrolysis Cell Research Articles

New insight into Na+-promoted microbial electrolysis cell towards hydrogen energy recovery: Feasibility and dual mechanism in salt-containing wastewater treatment

The salt-containing wastewater treatment has become serious challenge, while conductivity and micro-ecosystem disorder severely limited microbial electrolysis cell (MEC) efficiency. In order to synchronously overcome the above bottlenecks, this study proposed an innovative Na+-promoted MEC system for efficient salt-containing wastewater treatment. The Na+ presence greatly improved conductivity to impair electric resistance, resulting in rapid electron transfer pattern towards organic degradation in anode and hydrogen synthesis in cathode. Furthermore, the selective Na+ stress triggered microbial community evolution and improved electroactive bacteria activity after salinity cultivation in MEC (0.09–0.17 mol Na+/L), which played “bacteria screening” role for salt-tolerant “electrochemical hydrogen-producing” bacteria community formation. The organic-degrading and hydrogen-producing bacteria with their assistors were tolerant to Na+ stress, which were considerably enriched into dominant microorganisms, while the unfavorable bacteria responsible for hydrogen consumption and competition were inhibited due to salinity-sensitivity. Correspondingly, the metabolic pathways for metabolism, genetic information processing and environmental information processing were improved, positively associating with organic degradation and hydrogen production. Such dual driving contributions of Na+-improved electron transfer-utilization pattern and Na+-modified microbial metabolisms boosted the organic pollutant degradation at anode to 91.34 % while improving the performance and speeds of hydrogen production by 1.57–1.70 times. The hydrogen abundance was also increased to 71.57 % in biogas. The energy efficiencies relative to external electricity and substrates were elevated by 8.80–28.44 %, the coulombic efficiency raised by 14.05 % and reached 109.72 %, suggesting the positive net energy benefits. The findings provided inspirations to the feasible application of MEC in salt-containing wastewater treatment with efficiency benefits.

Scalable membrane-less microbial electrolysis cell with multiple compact electrode assemblies for high performance hydrogen production

Bioelectrochemical hydrogen production via microbial electrolysis cells (MECs) is a promising method for sustainable energy production and decarbonization of energy systems. However, the application of MECs is limited by the electrochemical performance, scalability, and the cost associated with expensive materials. In this study, a scalable MEC (500 mL) with novel compact electrode assemblies and high electrode surface area to volume ratio (160 m2/m3) was designed and constructed. The use of membranes, precious metal catalyst, and current collectors with high costs was avoided. A high current density at the steady state of 49.5 ± 5.3 A/m2 was achieved using acetate as the substrate with phosphate buffer under the applied voltage of 1.01 V. The corresponding volumetric current density was 3948 ± 422 A/m3. The compact electrode assembly design limited methane production rate to 3.9 ± 0.2 L/L/D, while achieving a hydrogen production rate of 33.7 ± 1.7 L/L/D. With the suppression of microbial hydrogen consumption, the hydrogen production rate was 39.8 ± 1.9 L/L/D, higher by almost one order of magnitude than those of MECs with scaling up attempts. The compact electrode configuration reduced internal resistance to 88.5 ± 4.4 Ω cm2. The energy efficiency based on input electricity was 146 ± 7 % to 189 ± 9 % within the applied voltage range of 0.71 to 1.05 V. The results in this study demonstrated successful scaling up of high performance small MECs and offered a new possible approach of scaling up MECs by stacking high-performance subunits, with no trade-offs on electrochemical performance.

High concentration of ammonia sensitizes the response of microbial electrolysis cells to tetracycline

Microbial electrolysis cell (MEC) is a promising technology for effective energy conversion of wastewater organics to biogas. Yet, in swine wastewater treatment, the complex contaminants including antibiotics may affect MEC performance, while the high ammonia concentration might increase this risk by increasing cell membrane permeability. In this work, the responses of MECs on tetracycline (TC) with low and high ammonia loadings (80 and 1000 mg L–1) were fully investigated. The TC of 0 to 1 mg L–1 slightly improved MEC performance in current production and electrochemical characteristics with low ammonia loading, while TC ≥ 4 mg L–1 started to show negative effects. Generally, the high ammonia loading sensitized MECs to TC concentration, inducing the current and COD removal of MECs to sharply decline with TC ≥ 0.5 mg L–1. The positive effect of high ammonia loading on MEC due to conductivity increase was counteracted with TC ≥ 1 mg L–1. The co-contamination of TC and ammonia significantly decreased the bioactivity and biomass of anode biofilm. Although the high concentration of co-existing TC and ammonia inhibited MEC performance, the reactors still obtained positive energy feedback. The network analyses indicated that the effluent suspension contributed much to antibiotic resistance gene (ARG) transmission, while the microplastics (MPs) in wastewater greatly raised the risks of ARGs spreading. This work systematically examined the synergetic effects of TC and ammonia and the transmission of ARGs in MEC operation, which is conducive to expediting the application of MECs in swine wastewater treatment.

Microbial Electrolysis Cell as a Diverse Technology: Overview of Prospective Applications, Advancements, and Challenges

Microbial electrolysis cells (MECs) have been explored for various applications, including the removal of industrial pollutants, wastewater treatment chemical synthesis, and biosensing. On the other hand, MEC technology is still in its early stages and faces significant obstacles regarding practical large-scale implementations. MECs are used for energy generation and hydrogen peroxide, methane, hydrogen/biohydrogen production, and pollutant removal. This review aimed to investigate the aforementioned uses in order to better understand the different applications of MECs in the following scenarios: MECs for energy generation and recycling, such as hydrogen, methane, and hydrogen peroxide; contaminant removal, particularly complex organic and inorganic contaminants; and resource recovery. MEC technology was examined in terms of new concepts, configuration optimization, electron transfer pathways in biocathodes, and coupling with other technologies for value-added applications, such as MEC anaerobic digestion, combined MEC–MFC, and others. The goal of the review was to help researchers and engineers understand the most recent developments in MEC technologies and applications.

Ammonium and Phosphate Recovery in a Three Chambered Microbial Electrolysis Cell: Towards Obtaining Struvite from Livestock Manure

Ammonia and phosphate, which are present in large quantities in waste streams such as livestock manure, are key compounds in fertilization activities. Their recovery will help close natural cycles and take a step forward in the framework of a circular economy. In this work, a lab-scale three-chambered microbial electrolysis cell (MEC) has been operated in continuous mode for the recovery of ammonia and phosphate from digested pig slurry in order to obtain a nutrient concentrated solution as a potential source of fertilizer (struvite). The maximum average removal efficiencies for ammonium and phosphate were 20% ± 4% and 36% ± 10%, respectively. The pH of the recovered solution was below 7, avoiding salt precipitation in the reactor. According to Visual MINTEQ software modelling, an increase of pH value to 8 outside the reactor would be enough to recover most of the potential struvite (0.21 mmol L−1 d−1), while the addition of up to 0.2 mM of magnesium to the nutrient recovered solution would enhance struvite production from 5.6 to 17.7 mM. The application of three-chambered MECs to the recovery of nutrients from high strength wastewater is a promising technology to avoid ammonia production through industrial processes or phosphate mineral extraction and close nutrient natural cycles.

Competition of two highly specialized and efficient acetoclastic electroactive bacteria for acetate in biofilm anode of microbial electrolysis cell

Maintaining functional stability of microbial electrolysis cell (MEC) treating wastewater depends on maintaining functional redundancy of efficient electroactive bacteria (EAB) on the anode biofilm. Therefore, investigating whether efficient EAB competing for the same resources (electron donor and acceptor) co-exist at the anode biofilm is key for the successful application of MEC for wastewater treatment. Here, we compare the electrochemical and kinetic properties of two efficient acetoclastic EAB, Geobacter sulfurreducens (GS) and Desulfuromonas acetexigens (DA), grown as monoculture in MECs fed with acetate. Additionally, we monitor the evolution of DA and GS in co-culture MECs fed with acetate or domestic wastewater using fluorescent in situ hybridization. The apparent Monod kinetic parameters reveal that DA possesses higher jmax (10.7 ± 0.4 A/m2) and lower KS, app (2 ± 0.15 mM) compared to GS biofilms (jmax: 9.6 ± 0.2 A/m2 and KS, app: 2.9 ± 0.2 mM). Further, more donor electrons are diverted to the anode for respiration in DA compared to GS. In acetate-fed co-culture MECs, DA (98% abundance) outcompete GS for anode-dependent growth. In contrast, both EAB co-exist (DA: 55 ± 2%; GS: 24 ± 1.1%) in wastewater-fed co-culture MECs despite the advantage of DA over GS based on kinetic parameters alone. The co-existence of efficient acetoclastic EAB with high current density in MECs fed with wastewater is significant in the context of functional redundancy to maintain stable performance. Our findings also provide insight to future studies on bioaugmentation of wastewater-fed MECs with efficient EAB to enhance performance.

Microbial electrolysis cells for electromethanogenesis: Materials, configurations and operations

Anaerobic digestion is a traditional method of producing methane-containing biogas by utilizing the methanogenic conversion of organic matter like agricultural waste and animal excreta. Recently, the application of microbial electrolysis cell (MECs) technology to a traditional anaerobic digestion system has been extensively studied to find new opportunities in increasing wastewater treatability and methane yield and producing valuable chemicals. The finding that both anodic and cathodic bacteria can synthesize methane has led to the efforts of optimizing multiple aspects like microbial species, formation of biofilms, substrate sources and electrode surface for higher production of the combustible compound. MECs are very fascinating because of its ability to uptake a wide variety of raw materials including untreated wastewater (and its microbial content as biocatalysts). Extensive work in this field has established different systems of MECs for hydrogen production and biodegradation of organic compounds. This review is dedicated to explaining the operating principles and mechanism of the MECs for electromethanogenesis using different biochemical pathways. Emphasis on single- and double-chambered MECs along with reactor components is provided for a comprehensive description of the technology. Methane production using hydrogen evolution reaction and nanocatalysts has also been discussed.

Comparison of hydrogen production and system performance in a microbial electrolysis cell containing cathodes made of non-platinum catalysts and binders

Microbial electrolysis cell (MEC) is an innovative electrochemical technology that decomposes organic matter in anode and produces hydrogen in cathode. It is imperative to use a high-performance and a low-cost cathode material to make the application of MEC economically viable. In this study, five different cathodes made of low-cost materials were tested in MECs. The materials included activated carbon (AC) and nickel powder (Ni) as a cathode catalyst; polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVDF) as a catalyst binder; stainless steel mesh (SSM) as a cathode substrate or a cathode itself. Among the tested cathodes, Ni/AC/PTFE obtained the best performance, followed by Ni/AC/PVDF, AC/PVDF, flamed-oxidized SSM (SSM/F) and SSM. Ni/AC/PTFE exhibited the best performance in hydrogen production rate (HPR, 1.88 L/L d), hydrogen purity (97.5%), coulombic efficiency (124%), energy efficiency (216%), cathodic capacitance (0.9924 F), along with the lowest cathodic impedance (35 Ω). The worst performed SSM showed as follows: 0.57 L/L d of HPR, 71% of hydrogen purity, 36% of coulombic efficiency, 62% of energy efficiency, 0.0008 F of cathodic capacitance and 62 Ω of cathodic impedance. This study shows quantitatively the electrochemical and performance transitions of MEC according to the cathode component changes.

Mo2N nanobelt cathodes for efficient hydrogen production in microbial electrolysis cells with shaped biofilm microbiome

High cost platinum (Pt) catalysts limit the application of microbial electrolysis cells (MECs) for hydrogen (H2) production. Here, inexpensive and efficient Mo2N nanobelt cathodes were prepared using an ethanol method with minimized catalyst and binder loadings. The chronopotentiometry tests demonstrated that the Mo2N nanobelt cathodes had similar catalytic activities for H2 evolution compared to that of Pt/C (10 wt%). The H2 production rates (0.39 vs. 0.37 m3-H2/m3/d), coulombic efficiencies (90% vs. 77%), and overall hydrogen recovery (74% vs. 70%) of MECs with the Mo2N nanobelt cathodes were also comparable to those with Pt/C cathodes. However, the cost of Mo2N nanobelt catalyst ($ 31/m2) was much less than that of Pt/C catalysts ($ 1930/m2). Furthermore, the biofilm microbiomes at electrodes were studied using the PacBio sequencing of full-length 16S rRNA gene. It indicated Stenotrophomonas nitritireducens as a putative electroactive bacterium dominating the anode biofilm microbiomes. The majority of dominant species in the Mo2N and Pt/C cathode communities belonged to Stenotrophomonas nitritireducens, Stenotrophomonas maltophilia, and Comamonas testosterone. The dominant populations in the cathode biofilms were shaped by the cathode materials. This study demonstrated Mo2N nanobelt catalyst as an alternative to Pt catalyst for H2 production in MECs.

Efficient hydrogen recovery with CoP-NF as cathode in microbial electrolysis cells

The emerging microbial electrolysis cell (MEC) is of great potential for energy recovery from wastewater as hydrogen, while the application of MECs required cost-effective, scalable cathodes. Here, the phosphating cobalt (CoP) acicular nanoarray in-situ growing on a 3D commercial nickel foam (NF) matrix without binder demonstrated outstanding electrocatalytic activity. The nano-CoP coated NF (CoP-NF) was assessed for hydrogen recovery performance in MEC. In electrochemical testing, the CoP-NF demonstrated comparable performance to a commercial Pt/C catalyst in linear scan voltammetry tests. The lower Tafel slope of 175.4 mV dec−1 in 1 M phosphate buffer electrolyte indicated more favorable electrochemical kinetics of CoP-NF than commercial Pt/C. The CoP-NF demonstrated higher electrochemical active surface area of electrode-liquid interface for its acicular nano-structure, while the smaller charge transfer resistance of CoP-NF suggested the faster electron transfer rate and catalytic activity of hydrogen evolution reaction. An improved hydrogen production rate of 222 ± 20.3 mL H2 L−1 d−1 at 0.7 V applied voltage in fully assembled MECs was achieved for the outstanding hydrogen evolution performance of CoP-NF cathode, which was 3-fold superior to bare NF and even better than the Pt/C. The energy efficiency based on input electricity in the MECs equipped with the CoP-NF (90 ± 6.5%) was increased to twice as much as that Pt/C based cathodes. Long-term operation tests of MECs confirmed the superior stability of CoP-NF as an effective cathode in MECs for hydrogen production, suggesting its potential possibility in practical application.

Selective inhibition of methanogenesis by acetylene in single chamber microbial electrolysis cells

Microbial electrolysis cells (MECs) for hydrogen production exhibit great advantages over many other biohydrogen production techniques in terms of versatility of substrate and hydrogen yield. However, hydrogen and acetate scavenging by methanogens puts forward a great challenge to the application of single chamber MECs when using mixed culture. In this study, we investigated the feasibility of using acetylene, a low-cost fuel and chemical building block, to selectively inhibit methanogenesis in single chamber MECs. Results demonstrate that the periodical injection of low concentration acetylene (1% and 5%) can successfully inhibit methanogenesis in MECs using both acetate and glucose as substrates. Current generation by exoelectrogens and the syntrophy between fermentative bacteria and exoelectrogens, however, were not negatively affected. Compared with the classic methanogen inhibitor, 2-Bromoethanesulfonate (BES), the low concentration acetylene demonstrates superior effectiveness in MECs. These results demonstrate the great potential of using acetylene as a cost-effective inhibitor against methanogenesis in MECs.

Platinum Group Metal-free Catalysts for Hydrogen Evolution Reaction in Microbial Electrolysis Cells.

Hydrogen gas is a green energy carrier with great environmental benefits. Microbial electrolysis cells (MECs) can convert low-grade organic matter to hydrogen gas with low energy consumption and have gained a growing interest in the past decade. Cathode catalysts for the hydrogen evolution reaction (HER) present a major challenge for the development and future applications of MECs. An ideal cathode catalyst should be catalytically active, simple to synthesize, durable in a complex environment, and cost-effective. A variety of noble-metal free catalysts have been developed and investigated for HER in MECs, including Nickel and its alloys, MoS2 , carbon-based catalysts and biocatalysts. MECs in turn can serve as a research platform to study the durability of the HER catalysts. This personal account has reviewed, analyzed, and discussed those catalysts with an emphasis on synthesis and modification, system performance and potential for practical applications. It is expected to provide insights into the development of HER catalysts towards MEC applications.

A novel tubular microbial electrolysis cell for high rate hydrogen production

Practical application of microbial electrolysis cells (MECs) for hydrogen production requires scalable reactors with low internal resistance, high current density, and high hydrogen recovery. This work reports a liter scale tubular MEC approaching these requirements. The tubular cell components (a platinum-coated titanium mesh cathode, an anion exchange membrane, and a pleated stainless steel felt anode) were arranged in a concentric configuration. The reactor had a low internal resistance (0.325 Ω, 19.5 mΩ m2) due to the high conductivity of the electrodes, a compact reactor configuration, and proper mixing. With acetate as electron donor, the MEC achieved a volumetric current density of 654 ± 22 mA L−1 (projected current density, 1.09 ± 0.04 mA cm−2) and a volumetric hydrogen production rate of 7.10 ± 0.01 L L−1 d−1 at an applied voltage of 1 V. The reactor also showed high hydrogen recovery (∼100%), high hydrogen purity (>98%), and excellent operational stability during the 3 weeks of operation. These results demonstrated that high hydrogen production rate could be achieved on larger scale MEC and this tubular MEC holds great potential for scaling up.

Ammonia recovery from urine in a scaled-up Microbial Electrolysis Cell

Abstract A two-step treatment system for nutrient and energy recovery from urine was successfully operated for six months. In the first step, phosphorus (P) was recovered as struvite (magnesium ammonium phosphate or MAP) in a MAP reactor. The effluent of this MAP reactor was used for total ammonia-nitrogen (TAN) recovery and hydrogen production in a Microbial Electrolysis Cell (MEC). This MEC was coupled to a Transmembranechemisorption (TMCS) module, in which the TAN was recovered as an ammonium sulphate solution. The MEC had a projected surface area of 0.5 m 2 and was operated at different urine dilutions. The system was stable during the operation on 2 times diluted and undiluted urine at an applied voltage of 0.5 V with an average current density of 1.7 ± 0.2 A m −2 . During stable current production, the TAN transport efficiency over the CEM was 92 ± 25% and the TAN recovery was 31 ± 59%. In terms of energy efficiency, the electrical energy required for the TAN recovery was 4.9 ± 1.0 MJ kg N −1 , which is lower than competing electrochemical nitrogen removal/recovery technologies. Overall, this study shows, for the first time, the application of a scaled-up MEC for nutrient recovery from urine.

Nickel-based electrodeposits as potential cathode catalysts for hydrogen production by microbial electrolysis

Abstract The development of cost-effective cathodes, operating at neutral pH and ambient temperatures, is a crucial challenge for the practical application of microbial electrolysis cell (MEC) technology. In this study, NiW and NiMo co-deposits produced by electroplating on Ni-foam are explored as cathodes in MEC. The fabricated electrodes exhibit higher corrosion stability and enhanced electrocatalytic activity towards hydrogen evolution reaction in neutral electrolyte compared to the bare Ni-foam. NiW/Ni-foam electrodes possess six times higher intrinsic catalytic activity, estimated from data obtained by linear voltammetry and chronoamperometry. The newly developed electrodes are applied as cathodes in single-chamber membrane-free MEC reactors, inoculated with wastewater and activated sludge from a municipal wastewater treatment plant. Cathodic hydrogen recovery of 79% and 89% by using NiW and NiMo cathodes, respectively, is achieved at applied voltage of 0.6 V. The obtained results reveal potential for practical application of used catalysts in MEC.

Microbial communities change in an anaerobic digestion after application of microbial electrolysis cells

Microbial electrolysis cells (MECs) are being studied to improve the efficiency of anaerobic digesters and biogas production. In the present study, we investigated the effects of electrochemical reactions in AD-MEC (anaerobic digester combined with MECs) on changes in the microbial communities of bulk sludge through 454-pyrosequencing analysis, as well as the effect of these changes on anaerobic digestion. Methanobacterium beijingense and Methanobacterium petrolearium were the dominant archaeal species in AD, while Methanosarcina thermophila and Methanobacterium formicicum were dominant in AD-MEC at steady-state. There were no substantial differences in dominant bacterial species. Clostridia class was more abundant than Bacteroidia class in both reactors. Compared to AD, AD-MEC showed a 40% increase in overall bacterial population, increasing the removal of organic matters and the conversion of volatile fatty acids (VFAs). Thus, the MEC reaction more effectively converts organic matters to VFAs and activates microbial communities favorable for methane production.

Application of microbial electrolysis cells to treat spent yeast from an alcoholic fermentation

Spent yeast (SY), a major challenge for the brewing industry, was treated using a microbial electrolysis cell to recover energy. Concentrations of SY from bench alcoholic fermentation and ethanol were tested, ranging from 750 to 1500mgCOD/L and 0 to 2400mgCOD/L respectively. COD removal efficiency (RE), coulombic efficiency (CE), coulombic recovery (CR), hydrogen production and current density were evaluated. The best treatment condition was 750mgCOD/LSY+1200mgCOD/L ethanol giving higher COD RE, CE, CR (90±1%, 90±2% and 81±1% respectively), as compared with 1500mgCOD/LSY (76±2%, 63±7% and 48±4% respectively); ethanol addition was significantly favorable (p value=0.011), possibly due to electron availability and SY autolysis. 1500mgCOD/LSY+1200mgCOD/L ethanol achieved higher current density (222.0±31.3A/m3) and hydrogen production (2.18±0.66 LH2/day/LReactor) but with lower efficiencies (87±2% COD RE, 71.0±.4% CE). Future work should focus on electron sinks, acclimation and optimizing SY breakdown.

Hydrogen production and wastewater treatment in a microbial electrolysis cell with a biocathode.

The broad application of microbial electrolysis cells (MECs) requires a system characterized by low cost and high operational sustainability. Biocathode MECs, which only require bacteria as the cathode catalysts, can satisfy these demands and have attracted considerable attention in recent years. In this study, we have examined biocathode alternatives to the typical platinum cathode in a single-chamber, membrane-free MEC. This biocathode MEC has been used for simultaneous hydrogen production and wastewater treatment. The results showed that hydrogen production rates increased in response to an increase in voltage. At an applied voltage of 0.9 V, the biocathode MEC achieved a hydrogen production rate of 0.39 m3 m(-3) d(-1), with a current density of 134 Am(-3), chemical oxygen demand (COD) removal of 90%, a coulombic efficiency of 63%, a cathodic hydrogen recovery of 37%, and an energy efficiency based on an electricity input of 67%. The biocathode demonstrated sufficient electrocatalytic activity and achieved a performance level comparable to that of the platinum cathode. Moreover, the substrate that was used to simulate wastewater in this study was efficiently treated by the MEC.

High hydrogen production rate of microbial electrolysis cell (MEC) with reduced electrode spacing

Practical applications of microbial electrolysis cells (MECs) require high hydrogen production rates and a compact reactor. These goals can be achieved by reducing electrode spacing but high surface area anodes are needed. The brush anode MEC with electrode spacing of 2 cm had a higher hydrogen production rate and energy efficiency than an MEC with a flat cathode and a 1-cm electrode spacing. The maximum hydrogen production rate with a 2 cm electrode spacing was 17.8 m(3)/m(3)d at an applied voltage of E(ap)=1 V. Reducing electrode spacing increased hydrogen production rates at the lower applied voltages, but not at the higher (>0.6 V) applied voltages. These results demonstrate that reducing electrode spacing can increase hydrogen production rate, but that the closest electrode spacing do not necessarily produce the highest possible hydrogen production rates.

Hydrogen production in single-chamber tubular microbial electrolysis cells using non-precious-metal catalysts

Platinum has excellent catalytic capabilities and is commonly used as cathode catalyst in microbial electrolysis cells (MECs). Its high cost, however, limits the practical applications of MECs. In this study, precious-metal-free cathodes were developed by electrodepositing NiMo and NiW on a carbon-fiber-weaved cloth material and evaluated in electrochemical cells and tubular MECs with cloth electrode assemblies (CEA). While similar performances were observed in electrochemical cells, NiMo cathode exhibited better performances than NiW cathode in MECs. At an applied voltage of 0.6 V, the MECs with NiMo cathode accomplished a hydrogen production rate of 2.0 m 3/day/m 3 at current density of 270 A/m 3 (12 A/m 2), which was 33% higher than that of the NiW MECs and slightly lower than that of the MECs with Pt catalyst (2.3 m 3/day/m 3). At an applied voltage of 0.4 V, the energy efficiencies based on the electrical energy input reached 240% for the NiMo MECs. These results demonstrated the great potential of using carbon cloth with Ni-alloy catalysts as a cathode material for MECs. The enhanced MEC performances also demonstrate the scale-up potential of the CEA structure, which can significantly reduce the electrode spacing and lower the internal resistance of MECs, thus increasing the hydrogen production rate.