Fuel Cell Architecture Research Articles

Hydrogen in aviation: A simulation of demand, price dynamics, and CO2 emission reduction potentials

Aviation contributes to anthropogenic climate change by emitting both carbon dioxide (CO2) and non-CO2 emissions through the combustion of fossil fuels. One approach to reduce the climate impact of aviation is the use of hydrogen as an alternative fuel. Two distinct technological options are presently under consideration for the implementation of hydrogen in aviation: hydrogen fuel cell architectures and the direct combustion of hydrogen. In this study, a hydrogen demand model is developed that considers anticipated advancements in liquid hydrogen aircraft technologies, forecasted aviation demand, and aircraft startup and retirement cycles. The analysis indicates that global demand for liquid hydrogen in aviation could potentially reach 17 million tons by 2050, leading to a 9% reduction in CO2 emissions from global aviation. Thus, the total potential of hydrogen in aviation extends beyond this, considering that the total market share of hydrogen aircraft on suitable routes in the model is projected to be only 27% in 2050 due to aircraft retirement cycles. Additionally, it is shown, that achieving the potential demand for hydrogen in aviation depends on specific market prices. With anticipated declines in current production costs, hydrogen fuel costs would need to reach about 70 EUR/MWh by 2050 to fulfill full demand in aviation, assuming biofuels provide the cheapest option for decarbonization alongside hydrogen. If e-fuels are the sole option for decarbonization alongside hydrogen, which is the more probable scenario, the entire hydrogen demand potential in aviation would be satisfied according to this study's estimates at significantly higher hydrogen prices, approximately 180 EUR/MWh.

Innovative lead-carbon battery utilizing electrode-electrolyte assembly inspired by PEM-FC architecture

This study explores the innovative integration of a lead‑carbon battery with an electrode-electrolyte assembly inspired by Proton Exchange Membrane Fuel Cell (PEM-FC) architecture. The lead‑carbon material, synthesized with a 40 % mass ratio using the Flash Joule Heating Method, exhibits predominant Pb0 and PbO phases, as observed in lattice parameter fringes, with additional detection of the PbO2 phase. The resulting Carbon-Lead Acid Battery (CLAB) demonstrates a specific capacity of 11.2 mAh g−1. The incorporation of carbon enhances nanoparticle stability, yielding a highly stable battery performance over 100 cycles, with discharge potential variations of <2 %. This innovative CLAB assembly not only showcases stable performance and also introduces the potential for constructing flexible lead batteries, expanding technological applications. The study provides comprehensive insights into the synthesis, performance, and prospects of this novel lead‑carbon battery architecture, emphasizing its significance in the realm of energy storage solutions.

Improved chaos grasshopper optimizer and its application to HRES techno-economic evaluation

Current political and economic trends are moving more and more toward the use of renewable and clean energy as a result of rising energy use and diminishing fossil fuel supplies. In this paper, an improved chaos-based grasshopper optimizer used for techno-economic evaluation in integrated green power systems is investigated. The integrated system consists of a fuel cell system, a wind farm, and solar energy. The integrated solar, wind, and hydrogen fuel cell architectures increase the effectiveness and electrical output of the system while needing less energy storage in structures that are unconnected from the grid. The grasshopper optimization technique and chaos theory have been combined to create the suggested chaotic grasshopper optimizer in this study. The performance, precision, and robustness of this optimization were then assessed, using four benchmark tasks. The ICGO model is utilized to assign suitable ratings to all system devices, thereby guaranteeing the attainment of optimal performance and efficiency. The Net Present Cost (NPC) analysis revealed that the ICGO algorithm attained the lowest minimum NPC value of 274.541E4 USD and the highest maximum NPC value of 311.94E4 USD. The average NPC value of the ICGO algorithm (289.176E4 USD) was found to be comparable to the other algorithms examined in the study. These findings indicate that the ICGO algorithm outperformed other optimization algorithms in minimizing the cost of the renewable energy system. The chaotic grasshopper optimizer can handle several targets, restrictions, and variables with ease, and the results demonstrate that it is substantially more efficient and precise than standard optimization techniques. It is also quite durable, with minimal performance degradation as compared to the benchmark solutions. This study demonstrates the effectiveness of the chaos grasshopper optimizer as an HRES technique.

Power equalizer for a series fuel cell architecture based on load tracking control

This paper analyses the safe operation of a multi-stack Polymer Electrolyte Membrane Fuel Cell (PEMFC) under normal conditions and partial faults using an innovative power-sharing technique based on Load-Following (LF) control. LF control references are designed based on the power flow balance to track the dynamic load profile. These references control the power flow of DC-DC boost converters connected to PEMFC stacks, performing power sharing and output voltage restoration as a final result. The behavior of multi-stack FC architecture is presented in conditions of partial drying and flooding of PEMFCs. If the transitory faults are short, the controllability of the boost converters is ensured by LF control and multi-stack FC architecture continues to safety operate in degraded-operation mode.

Performance evaluation of porous gas channel ribs in a polymer electrolyte fuel cell

Commercialization of hydrogen fuel cells is scaling at an unprecedented rate. As a result, developers are focused on stack manufacturability and the associated challenges to scaling-up an assembly with thousands of individual parts that have strict dimensional tolerances. This paper first proposes a fuel cell architecture designed for continuous manufacturing that could result in all components of a stack being contained in a rolled good. This concept would move the reactant gas distribution channels into the gas diffusion substrate. The performance of the porous ribs that would result from this concept is compared with a conventional solid rib flow distributor. Performance and cell resistance are presented in a series of single factor experiments that investigate a wide PEMFC operating space. The results show that a porous rib cathode flow field is feasible, with performance benefits at near- and over-saturated operating conditions.

Adhesion of Nafion for advanced proton exchange membrane fuel cell architectures under low fabrication temperature

AbstractNafion has been used as one of the essential materials for proton exchange membrane fuel cells. The ability to laminate Nafion to itself and other materials, to form hermetic seals, leads to novel architectures, including a device designed by our group. In this work, understanding of cohesion/adhesion is essential because the sealing relies on interfacial properties of the materials. Since the ionic character of Nafion is known to be sensitive to processing temperature, it is essential to understand what regimes of processing conditions lead to a good device operation while providing robust sealing. To characterize cohesion/adhesion strength and understand the correlation with fabrication, the T‐peel test was applied. Results show that the bonding strengths of Nafion–Nafion increase sharply with processing temperature. More dramatically, the presence of an interposed aluminum layer further increases the strength by up to a factor of 100 for processing temperatures below 140°C. Scanning electron microscopy and X‐ray photoelectron spectroscopy were used to characterize the resulting surfaces and to evaluate the surface chemistry of the delaminated Nafion–Al joints. The bonding across the interface was enhanced by formation of Al–F and O–Fx bonds as a result of the introduction of Al. Adhesion strength increases as the preponderance of the two types changes with the bonding temperature.

Hydrogen Fuel Cell and Battery Hybrid Architecture for Range Extension of Electric VTOL (eVTOL) Aircraft

The objective of this paper is to study the impact of combining hydrogen fuel cells with lithium-ion batteries through an ideal power-sharing architecture to mitigate the poor range and endurance of battery powered electric vertical takeoff and landing (eVTOL) aircraft. The benefits of combining the two sources is first illustrated by a conceptual sizing of an electric tiltrotor for an urban air taxi mission of 75 mi cruise and 5 min hover. It is shown that an aircraft of 5000–6000 lb gross weight can carry a practical payload of 500 lb (two to three seats) with present levels of battery specific energy (150 Wh/kg) if only a battery–fuel cell hybrid power plant is used, combined in an ideal power-sharing manner, as long as high burst C-rate batteries are available (4–10 C). A power plant using batteries alone can carry less than half the payload; use of fuel cells alone cannot lift off the ground. Next, the operation of such a system is demonstrated using systematic hardware testing. The concepts of unregulated and regulated power-sharing architectures are described. A regulated architecture that can implement ideal power sharing is built up in a step-by-step manner. It is found only two switches and three DC-to-DC converters are necessary, and if placed appropriately, are sufficient to achieve the desired power flow. Finally, a simple power system model is developed, validated with test data and used to gain fundamental understanding of power sharing.

Cu-substituted La2NiO4+δ as oxygen electrodes for protonic ceramic electrochemical cells

Abstract In order to overcome different tasks related to the thermal and chemical compatibility of functional solid oxide electrochemical cell materials, including those based on proton-conducting electrolytes, the search for new potential oxygen/steam electrodes is of great interest. In the present work, the Lа2Ni1–хCuxO4+δ (LNCx, x = 0. 0.1, 0.2 and 0.3) compounds, which constitute a class of Co-free and alkaline-earth elements (AEE)-free layered materials, were successfully synthesised and then studied as possible oxygen electrodes for protonic ceramic fuel cells. A complex of methods was used to comprehensively analyse the individual characteristics of LNCx (structural parameters, oxygen overstoichiometry, thermal expansion, total conductivity) as well as their properties in symmetrical and fuel cell architectures (polarisation resistance, performance). According to the obtained results, a slight degree of Ni with Cu substitution can be used for optimising the functional properties of LNCx, such as low sintering temperatures of cathode formation, low thermal expansion coefficients, good electronic conductivity and sufficient electrochemical activity (including under conditions of moisturised atmospheres). Therefore, the LNCx cathodes can be considered as one of the possible Co- and AEE-free candidates for intermediate-temperature protonic ceramic electrochemical cells.

Challenges of Microbial Fuel Cell Architecture on Heavy Metal Recovery and Removal From Wastewater

Being constituents of the effluents of many industries, heavy metals cause severe environmental pollution due to their recalcitrance and persistence in the environment. Conventional remediation strategies used to treat heavy metals loaded wastewater are neither economical nor environmentally friendly. To overcome these challenges, the rise of a new process that combines energy conservation and recovery was mandatory. Microbial fuel cells have been recognized as an emerging technology to mitigate environmental pollution; it provides a solution to wastewater treatment and the removal and/or recovery of heavy metals. Microbial fuel cells can be defined as bioelectrochemical systems that utilize the catalytic activity of microorganisms organized in biofilms to oxidize organic or inorganic compounds by producing electric current thus providing a new opportunity for sustainable energy production and bioremediation. The removal of metals, such as chromium, vanadium, arsenic, copper, silver and gold has been studied using both single and double chambered MFCs. The fact that some heavy metals have high redox potential makes it possible to utilize them as effective electron acceptors instead of oxygen in the cathodic chamber of microbial fuel cells. Biotic/Abiotic cathode chambers can not only remove but also recover heavy metals. However, a number of challenges such us: low production rates and limited efficiencies make the application of this technology restricted to lab scale only. In this chapter, we review the treatment of metal-containing effluents using microbial fuel cells. We’ll first summarize the principle of metal removal/recovery in microbial fuel cells, and then provide an overview of literature that attempted to treat metal loaded effluents in both single and double chambered microbial fuel cells while discussing power output, heavy metal removal efficiency and mechanisms involved in the process. Furthermore, the primary challenges and opportunities for scaling-up of microbial fuel cells and their future applications in the treatment of heavy metals contaminated wastewater will be outlined.

Thermal Management in a Half-MEA Microscale Fuel Cell Architecture

With the advancement of portable technology, suitable power sources must be developed. In comparison to standard battery technology, microscale fuel cells demonstrate higher energy densities and the potential for nearly instantaneous recharging [1]. However, fuel cells are commonly less efficient than batteries, and thusly, produce more waste heat. Waste heat is generated in methanol polymer electrolyte membrane fuel cells via the oxygen reduction reaction, the methanol oxidation reaction, and ohmic heating in the membrane. The oxygen reduction reaction accounts for the vast majority of the total heat generated [2]. Consequently, heat generation and removal in conventional fuel cell architectures has been carefully investigated in order to achieve effective thermal management [3]. Here we present a novel microscale fuel cell design that utilizes a half-membrane electrode assembly (MEA). In this design, a single fuel/electrolyte stream provides an additional pathway for heat removal that is not present in traditional fuel cell architectures. There are three streams in this fuel cell design: methanol fuel, oxygen, and nitrogen. Previously a simplified model neglecting the heat transfer through the anode side and nitrogen stream has been investigated [4]. The simplified model only has one heat generation source in the cathode catalyst. The ANSYS Fluent model presented here investigates heat removal of inlet fuel temperatures of 22°C, 40°C, 50°C, 60°C, and 70°C. This new model simulates the complete fuel cell including the anode side and nitrogen stream. There are three heat generation sources in the new model: oxygen reduction in the cathode catalyst, methanol oxidation in the anode catalyst, and ohmic heating in the membrane. Continuity, momentum, and energy equations were solved simultaneously by ANSYS Fluent to obtain the results. Heat generation densities are determined experimentally for all inlet fuel temperatures. The simulations predict thermal profiles throughout this microscale fuel cell design. The exit temperature of the fuel stream, oxygen stream, and nitrogen stream were obtained to determine the rate of heat removal. Simulation results show that the fuel stream dominates heat removal at room temperature. As inlet fuel temperature increases, the majority of heat removal occurs via convection with the ambient air by the exposed current collector surfaces. The top and bottom current collector removes nearly the same amount of heat. The model also shows that heat transfer through the oxygen channel and nitrogen channel is minimal over the range of inlet fuel temperatures. Ultimately, these simulations can be used to determine design points for best performance and durability in a single-channel microscale fuel cell. [1] M.A. Goulet, E. Kjeang, Journal of Power Sources, 260 (2014) 186-196. [2] A.Z. Weber, J. Newman, Journal of the Electrochemical Society, 153 (2006) A2205-A2214. [3] H. Ju, H. Meng, C-Y. Wang, International Journal of Heat and Mass Transfer, 48 (2005) 1303-1315. [4] L. Sun, A.S. Hollinger, ASME 2017 15th International Conference on Fuel Cell Science, Engineering and Technology, V001T03A001-V001T03A001. Figure 1

Batteries and Fuel Cells with Convective Mobile Electrolyte

Novel cost effective mobile electrolyte secondary battery and fuel cell architecture is proposed using tested properties of advanced materials. Otherwise high functioning historic fuel cell issues are potentially solved. Electrolyte circulation in BOP is simplified whereby multiple unit-cells connected in series for high voltage no longer discharge along fluid pathways. Active cores are compact, having high energy to weight and volume ratio. Forced convective permeability exceeds 20 Darcy at 1 cp viscosity for fluid velocity above 1 cm/sec. Direct-oxidation of suitable hydrocarbon fuels is virtually complete within the anode and convection of concentrated cation within the cathode accelerates ORR to improve O2 breathing in LIB and other faradaic and catalytic chemistries. These benefits are possible only when ultralow resistance electrodes, comprising porous cohesive nonwoven CNT membranes as a substrate, are uniquely attached to metal current collectors more fully described in a supplement following the main article.

An efficient auxiliary system controller for Fuel Cell Electric Vehicle (FCEV)

This article presents analysis of the systems in a Fuel Cell Electric Vehicle (FCEV) prototype with the aim of determining if it is possible to increase vehicle efficiency through strategic control of the auxiliary systems. To accomplish this, an overview of the vehicle design is given as well as an in depth analysis of the powertrain efficiency and control strategy. This leads to the development of a modified powertrain control algorithm which also oversees and controls the auxiliary power demand in real-time. The auxiliary control aspect of this algorithm follows predefined rules as determined through analysis of the individual systems, and based on the definitions of flexible useful and wasteful auxiliary power. The simulation results show that the proposed technique, applied to FCEV air conditioning system alone, improves the fuel economy in the neighborhood of 3.4% compared to conventional bang-bang controller. This magnitude of energy reduction is very significant in the automotive industry, especially when considering the number of vehicles in use in today's transportation sector. The resulting algorithm is adaptable to a number of different types of auxiliary systems and primary power sources, thereby not specifically tied to the fuel cell architecture for which it is developed.

State of the Art First Principles Computational Evaluation of Electrochemical Stability of a Nano-Scale Catalyst

Understanding and controlling the electrochemical stability of nanometerscale catalyst is vital for securing long-term operation of fuel cells. Novel proporty of the increased surface to volume ratio achieved by particle size reduction leads to lower materials cost and higher efficiency, but there are questions as to whether the intrinsic stability of materials also decreases with particle size. In this presentation it is shown that state of the art ab initio computational electrochemistry enables us to to construct Pourbaix diagrams of nano-scale Pt catalysts which determines the stability, passivation, and dissolution behavior as a function of particle size and potential. These results identify underlying mechanism controlling the electrochemical stability of nanoparticles and thus, propose how to design durable catalysts in fuel cell architectures.

Demonstration of a Reactive Hydrogen Pump Using Methanol

Polymer electrolyte membrane (PEM) fuel cells are an attractive energy conversion device because of the potential for extremely high efficiency and low emissions. Hydrogen is an ideal fuel for PEM fuel cells but it is energy intensive to produce.Currently the main method of producing hydrogen is steam reforming of natural gas. This is a break from the renewable energy future promised by hydrogen fuel cells. The most obvious method of producing hydrogen is water electrolysis but that is highly energy intensive since the electrolysis requires greater than the theoretical voltage of 1.23 V and thus is somewhat inefficient. To fulfill the promise of fuel cells, less energy intensive methods of producing hydrogen must be found.Here we describe some initial exploration of the concept of replacing water in the anode electrolyzer feed with a feedstock from which hydrogen can be stripped and purified in a combined electrochemical reactor. As a first step in testing this concept, we use methanol as the feed. Oxidation of methanol to hydrogen takes place at a theoretical voltage of .03 V. This is a significantly lower over-potential than water electrolysis and since most of the operating cost is energy, it has the potential to be significantly cheaper. Of course, the methanol oxidation reaction requires substantial overpotential because of sluggish kinetics but this is only an initial study.We constructed a methanol water electrolyzer based the conventional direct methanol fuel cell architecture as shown in Figure 1. The electrolysis cell uses a Pt-Ru black catalyst in the anode and a Pt cathode with a Nafion 117 membrane. We examined the effects of several different catalyst loadings, back-pressures, temperatures, and humidity levels. Finally, we utilized electrochemical impedance spectroscopy (EIS) and a dynamic hydrogen electrode (DHE) to more accurately determine the effectiveness of the catalysis and sources of voltage loss. Figure 2 shows an initial polarization curve obtained with this cell. Hydrogen was chosen for the working electrode and methanol for the counter electrode. The counter electrode potential stays fairly steady as does the ASR, while the working and cell potentials depend somewhat on the current being drawn. Increasing polarization of the working electrode begins to have a negative effect on cell current after .6V vs DHE. Acknowledgements We gratefully acknowledge the support of the Office of Naval Research for this activity. ReferencesC. Cloutier and D. Wilkinson, International Journal of Hydrogen Energy., 35,9,(2010)S. Thomas, X. Ren, S. Gottesfeld and P. Zelenay, Electrochimica Acta., 47 (2002)

Synergistic electrochemical activity of titanium carbide and carbon towards fuel cell reactions

Titanium carbide (TiC) is an electrically conducting refractory interstitial compound possessing several unique properties. A cost-effective, efficient and non-Pt electrocatalyst based on TiC is explored and the multi-functionality of TiC towards various electrochemical reactions that are of significant interest in low temperature fuel cells is studied. Ameliorated activities towards oxygen reduction reaction (ORR) and borohydride oxidation are observed with TiC–carbon composites. High sensitivity and selectivity towards ORR have been demonstrated with very good methanol tolerance. The charge transfer interactions between TiC and carbon seem to play a vital role in the improved activity as compared to their individual counterparts. The present study opens up a way to realize completely Pt-free borohydride fuel cell architecture.

Nanofluidic fuel cell

Fuel cells are gaining momentum as a critical component in the renewable energy mix for stationary, transportation, and portable power applications. State-of-the-art fuel cell technology benefits greatly from nanotechnology applied to nanostructured membranes, catalysts, and electrodes. However, the potential of utilizing nanofluidics for fuel cells has not yet been explored, despite the significant opportunity of harnessing rapid nanoscale reactant transport in close proximity to the reactive sites. In the present article, a nanofluidic fuel cell that utilizes fluid flow through nanoporous media is conceptualized and demonstrated for the first time. This transformative concept captures the advantages of recently developed membraneless and catalyst-free fuel cell architectures paired with the enhanced interfacial contact area enabled by nanofluidics. When compared to previously reported microfluidic fuel cells, the prototype nanofluidic fuel cell demonstrates increased surface area, reduced activation overpotential, superior kinetic characteristics, and moderately enhanced fuel cell performance in the high cell voltage regime with up to 14% higher power density. However, the expected mass transport benefits in the high current density regime were constrained by high ohmic cell resistance, which could likely be resolved through future optimization studies.

Borohydride-tolerant oxygen electroreduction catalyst for mixed-reactant Swiss-roll direct borohydride fuel cells

A novel and highly active Fe–aminoantipyrine (Fe–AAPyr) catalyst for oxygen reduction reaction (ORR) in alkaline media was synthesized by the modified sacrificial support method (SSM) and investigated in an innovative Swiss-roll mixed-reactant alkaline fuel cell architecture. The prepared Fe–AAPyr cathode showed excellent shorter-term (up to 200 min) durability and tolerance to electrooxidation of NaBH4. The Swiss-roll mixed-reactant Direct Borohydride Fuel Cell (DBFC) equipped with a Pt 3D anode and Fe–AAPyr gas-diffusion cathode produced an open circuit voltage and peak power density of 0.97 V and 137 mW cm−2 respectively at 45 °C and ambient pressure. These values are among the highest open circuit voltages and peak power densities reported for any mixed-reactant low temperature fuel cell and conventional dual chamber DBFCs.

Use of anode barrier layers in tubular solid-oxide fuel cells for robust operation on hydrocarbon fuels

This paper presents a unique demonstration of anode barrier-layer technology in a tubular solid-oxide fuel cell (SOFC) architecture. The anode barrier layer is a chemically inert, porous ceramic tube that is positioned within the inside diameter of the tubular SOFC, separating the catalytically active anode from the hydrocarbon-carrying fuel stream. This porous tube reduces the respective diffusion rates of reactants and products into and out of the anode. This increases the local concentration of electrochemically produced steam and carbon dioxide throughout the anode, resulting in higher local steam-to-carbon ratios that enhance the selectivity of internal-reforming reactions toward hydrogen and carbon monoxide over the formation of deleterious carbon deposits. In this study, stable electrochemical performance is demonstrated under a simulated “biogas” fuel stream (63% CH4/34% CO2/3% H2O) over 12 days of continuous operation. The performance of the barrier layer-equipped SOFC is characterized under biogas and hydrogen fuels, and compared to the performance of an SOFC without a barrier layer. While some decrease in power density is evident with the presence of a barrier layer, the performance decrease at 0.7V is modest. Morphological characterization after performance testing reveals no evidence of carbon deposition within the anode or barrier layer. These results demonstrate the potential of barrier-layer technology in tubular solid-oxide fuel cell architectures.

Biofilm conductivity is a decisive variable for high-current-density Geobacter sulfurreducens microbial fuel cells

Current outputs of microbial fuel cells (MFCs) are too low for most perceived practical applications. Most efforts for further optimization have focused on modifications of fuel cell architecture or electrode materials, with little investigation into the properties of microorganisms that are most essential for maximal current production. Geobacter sulfurreducens produces the highest current densities of any known pure culture; is closely related to the Geobacter species that often predominate in anode biofilms harvesting electricity from organic wastes; and produces highly conductive anode biofilms. Comparison of biofilm conductivities and current production in different strains of G. sulfurreducens revealed a direct correlation between biofilm conductivity and current density. Electrochemical impedance spectroscopy measurements demonstrated that higher biofilm conductivity not only reduced resistance to electron flow through the biofilm, but also lowered the activation energy barrier for electron transfer between the biofilm and the anode. These results demonstrate the crucial role of biofilm conductivity in achieving high current density in MFCs and suggest that increasing biofilm conductivity can boost MFC performance.

Performance Analysis of a Proton Exchange Membraneless Biological Fuel Cell Based on Lactate Dehydrogenase

Fuel cells with enzyme-coated electrodes, commonly known as enzymatic fuel cells, are closely looked at as a means to power implantable medical devices and miniaturized bioelectronic devices such as biomicroeletromechanical or nanoelectromechanical systems (bioMEMS/NEMS). This study attempts to develop a fuel cell with the proton exchange membrane (PEM) totally replaced by an enzyme coating tethered only to one electrode (anode). It was conjectured that the specificity of the enzyme to only a specific substrate at the anode coupled with the selectivity of reactions that could occur at the cathode due to thermodynamic preferences will discourage crossover reactions, making the PEM elimination possible. In the anode, lactate dehydrogenase (LDH), a NAD-dependent oxidoreductase, was immobilized on a gold-coated electrode using a layer-by-layer assembly technique. The LDH-coated anode catalyzed the oxidation of lactate to pyruvate, while Pt was used to catalyze the reduction of oxygen to water. Three parameters were selected to elucidate the behavior of the fuel cell under different load conditions. These parameters (lactate concentration, fuel cell temperature, and feed flow rate) were varied within the human physiological range to evaluate the performance as an implantable fuel cell. The cell reported an average open-circuit voltage of 261.72 0.01 mV, power density of 360.6 nW cm-1, and voltage efficiency of 25.05%. This experiment demonstrated that total elimination of the PEM is possible via coating only one electrode with a substrate-specific enzyme. This is a significant step toward developing power supplies for bioelectronic devices via enzymatic fuel cells, since elimination of the PEM enables unprecedented simplification of the fuel cell architecture (for miniaturization) while eliminating a component that contributes to significant internal resistance.