Direct Methanol Fuel Cell System Research Articles

(Invited) Solving the Energy Storage and Energy Conversion Conundrum – Materials to the Rescue

Energy storage systems have witnessed a meteoric rise ever since Sony commercialized the first Li-ion battery in 1994. Over the years, there have been a plethora of cathode, anode and electrolyte systems developed with stable cycle life and high coulombic efficiencies currently deployed in commercial electric vehicles. Similarly, alternate silicon and tin anodes were targeted as the next generation anodes to ubiquitous carbon. Recalcitrant volume expansion and ensuing solid electrolyte interphase (SEI) issues have reverted the focus back to the omnipresent high-energy density Li metal with efforts to overcome the ominous flammability and safety issues. Escalated impending demand for higher energy density have also made sulfur, an economic and common industrial effluent an attractive active material reverting attention back to Li-S batteries. Similarly, the portentous signs of global warming and the concomitant desire for developing green energy solutions have made hydrogen an imperative and attractive energy source providing the impetus for economic proton exchange membrane (PEM)-based water electrolysis (PEMWE) and fuel cells (PEMFCs). Like the energy storage field, PEMWE and PEMFCs have also witnessed intense research activity over the years following the early work on direct methanol fuel cells (DMFC). Developing high performance materials systems for energy storage and super responsive low-cost electrocatalysts still remain the major conundrum for developing high energy density and high-power density energy storage and conversion systems, respectively.This presentation will discuss the materials challenges that need to be overcome in Li-S batteries and PEM-based water electrolysis and fuel cells. Specifically, efforts aimed at achieving high-energy density cathodes and anodes as well as electrolyte additives for meeting the 500 Whkg-1 energy density targets for electric vehicle technology will be discussed. High sulfur (4-6 mg/cm2) loaded confined cathodes with unique ability to trap the pernicious polysulfide species combined with unique theoretical first principles calculations derived functional electrocatalysts exhibiting the propensity to reversibly catalyze the formation of Li2S and elemental S will be discussed. In tandem, progress made in generating new dendrite-free anodes and low-density current collectors exhibiting areal capacities as high as 15 mAh/cm2 with stable cycling over 100 cycles as well as electrolyte additives matching the cathode and anode performances will be outlined. Similarly, the journey into developing innovative low temperature chemical complexation approaches to novel bifunctional metallic nanostructured electrocatalysts first for DMFC systems and later how the unique approaches were modified targeting acid mediated PEMWE and PEMFCs comprising nanoscale metallic and complex ceramic doped oxide systems will be presented and discussed. Specifically, efforts made in the direction of realizing a unitized regeneration fuel cell (URFC) systems will be outlined and discussed in detail.

Green and sustainable use of macadamia nuts as support material in Pt-based direct methanol fuel cells

The successful commercialization of direct methanol fuel cells (DMFCs) is hindered by inadequate methanol oxidation activity and anode catalyst longevity. Efficient and cost-effective electrode materials are imperative in the widespread use of DMFCs. While Platinum (Pt) remains the primary component of anodic methanol oxidation reaction (MOR) electrocatalysts, its utilization alone in DMFC systems is limited due to carbon monoxide (CO) poisoning, instability, methanol crossover, and high cost. These limitations impede the economic feasibility of Pt as an electrocatalyst. Herein, we present the use of powdered activated carbon (PAC) and granular activated carbon (GAC), both sourced from macadamia nut shells (MNS), a type of biomass. These bio-based carbon materials are integrated into hybrid supports with reduced graphene oxide (rGO), aiming to enhance the performance and reduce the production cost of the Pt electrocatalyst. Electrochemical and physicochemical characterizations of the synthesized catalysts, including Pt-rGO/PAC-1:1, Pt-rGO/PAC-1:2, Pt-rGO/GAC-1:1, and Pt-rGO/GAC-1:2, were conducted. X-ray diffraction analysis revealed crystallite sizes ranging from 1.18 nm to 1.68 nm. High-resolution transmission electron microscopy (HRTEM) images with average particle sizes ranging from 1.91 nm to 2.72 nm demonstrated spherical dispersion of Pt nanoparticles with some agglomeration across all catalysts. The electrochemical active surface area (ECSA) was determined, with Pt-rGO/GAC-1:1 exhibiting the highest ECSA of 73.53 m2 g−1. Despite its high ECSA, Pt-rGO/GAC-1:1 displayed the lowest methanol oxidation reaction (MOR) current density, indicating active sites with poor catalytic efficiency. Pt-rGO/PAC-1:1 and Pt-rGO/PAC-1:2 exhibited the highest MOR current densities of 0.77 mA*cm−2 and 0.74 mA*cm−2, respectively. Moreover, Pt-rGO/PAC-1:2 and Pt-rGO/PAC-1:1 demonstrated superior electrocatalytic mass (specific) activities of 7.55 mA/mg (0.025 mA*cm−2) and 7.25 mA/mg (0.021 mA*cm−2), respectively. Chronoamperometry tests revealed Pt-rGO/PAC-1:2 and Pt-rGO/PAC-1:1 as the most stable catalysts. Additionally, they exhibited the lowest charge transfer resistances and highest MOR current densities after durability tests, highlighting their potential for DMFC applications. The synthesized Pt supported on PACs hybrids demonstrated remarkable catalytic performance, stability, and CO tolerance, highlighting their potential for enhancing DMFC efficiency.

Adaptive Joint Multiobjective Operating Parameters’ Optimization for Active Direct Methanol Fuel Cells

The operating parameters of the active direct methanol fuel cell (DMFC) are essential factors affecting its power delivery performance. Different operating parameters lead to variations in the amount of methanol crossover in a DMFC, which might cause overpotential and cathode catalyst poisoning. Due to the complexity of the DMFC system, changes in operating conditions, and correlations among these parameters, it is challenging to maintain output power density while reducing the negative effects of methanol crossover. This paper proposes an adaptive joint optimization method for fuel cell operating parameters. The principle operating parameters are selected by the orthogonal tests, which include an adaptive numerical simulation and multiobjective optimization regarding cell output power density and methanol crossover. The selected parameter combinations are verified by an evaluation model that quantifies the influences of operating parameters on the active DMFC power density and its methanol crossover, where the nonlinear mapping function for the two optimization objectives is obtained. The nondominated sorting genetic algorithm‐II (NSGA‐II) is applied to rapidly obtain the optimal combination. The results show that with the optimal parameters, the maximum power density is increased by 16.7% and the methanol crossover is reduced by 35.1%.

Improve methanol efficiency for direct methanol fuel cell system via investigation and control of optimal operating methanol concentration

This study investigates and controls the optimal operating methanol concentration for direct methanol fuel cell (DMFC) system, which effectively improves the efficiency of DMFC system. Firstly, a DMFC output characteristic model and a nonlinear stack methanol concentration model were established. Moreover, an adaptive observer was developed to reconstruct unmeasurable stack methanol concentration to estimate methanol concentration. Then, in order to achieve the minimum methanol consumption under required power, the reference methanol concentration was determined by analyzing DMFC system with its maximum energy conversion efficiency. Finally, the sliding mode algorithm was adopted to track reference optimal methanol concentration. The estimated performance of adaptive observer and non-adaptive observer for methanol concentration was compared through experimental bench data. Furthermore, the methanol consumption and energy conversion efficiency under proposed optimal methanol concentration strategy and fixed methanol concentration were compared. The comprehensive result demonstrates that the adaptive observer has better performance than non-adaptive observer in terms of estimated performance. Moreover, the proposed strategy for optimal methanol concentration was compared with fixed methanol concentration of 0.3 mol/L and 0.4 mol/L, and the fuel consumption of DMFC system was reduced by 7.9% and 30.9% respectively.

Technical and economic feasibility of applying fuel cells as the power source of unmanned aerial vehicles

This study aims to quantitatively compare the weight, cost, and flight endurance of small unmanned aerial vehicles (UAVs) powered by batteries and fuel cells. We compare the use of lithium-polymer (LiPo) batteries, proton exchange membrane fuel cells (PEMFCs), and direct methanol fuel cells (DMFCs) in powering two representative small UAVs: KHawk-Thermal (fixed-wing, 1.4 m wingspan) and KHawk-CarbonQuad (quadcopter, 0.7 m diagonal length). This study uses experimentally measured polarization curves of fuel cells and power consumption data of LiPo-powered UAVs during flight tests as input to obtain the minimum mass, power consumption, and life cycle costs (LCC) of these power systems. The analyses consider the voltage, efficiency, and power at each current density to find the optimal operating current density to obtain the minimum weight and cost of fuel cell systems to obtain the desired flight endurance. The LiPo battery is the most cost-effective option to power UAVs with an endurance of 0.7 hrs (42 min) or less. At medium flight endurance (e.g., 0.8 – 2.1 hrs), the PEMFC system has the lowest mass and LCC. While hydrogen is the most energy-dense fuel, hydrogen storage significantly increases the mass and cost of the system. For UAVs undergoing long endurance missions (>2.2 hrs for fixed-wing UAVs, > 4.3 hrs for quadcopter UAVs), a DMFC system has the lowest mass and power consumption due to the high energy density of methanol and its simple storage requirements. This study also analyzes the impact of key parameters, such as the specific energy and power of battery and fuel cells, the mass ratio of hydrogen storage, and the lift-to-drag ratio, on UAVs' mass and power consumption.

Nanocomposite of Electrochemically Reduced Graphene Oxide and Poly (p‐aminobenzenesulfonic acid) Incorporated with Ni (II) Ions as an Electrocatalyst for the Oxidation of Methanol

AbstractA new nanocomposite containing Ni(II) ions, electrochemically reduced graphene oxide (ERGO) and poly (p‐aminobenzenesulfonic acid) (Pp‐ABSA) on pencil graphite electrode (PGE) was prepared using electrochemical deposition coupled with self‐assembly accumulation method and characterized with different techniques. The electrochemical behavior and electrocatalytic activity of modified PGEs were investigated. The Ni/Pp‐ABSA/ERGO/PGE showed a unique electrocatalytic oxidation through an Electrochemical‐Chemical (EC’) pathway for methanol in alkaline media (Jpf=7.04 mA cm−2 and Eonest=0.38 V) compared to Ni/PGE, Ni/Pp‐ABSA/PGE and Ni/ERGO/PGE. The obtained results showed that the self‐assembled incorporation of Ni(II) ions in Pp‐ABSA/ERGO film prepared on PGE surface produced a stable modifier with high electrocatalytic activity towards methanol oxidation. In conclusion, the introduced method for the preparation of Pp‐ABSA/ERGO‐based nanocomposites can open a new, cheap and simple way to design a high‐performance electrocatalyst for direct methanol fuel cell systems.

Regulating local coordination environment of Mg−Co single atom catalyst for improved direct methanol fuel cell cathode

Fuel cells operated with a reformate fuel such as methanol are promising power systems for portable electronic devices due to their high safety, high energy density and low pollutant emissions. However, several critical issues including methanol crossover effect, CO-tolerance electrode and efficient oxygen reduction electrocatalyst with low or non-platinum usage have to be addressed before the direct methanol fuel cells (DMFCs) become commercially available for industrial application. Here, we report a highly active and selective Mg−Co dual-site oxygen reduction reaction (ORR) single atom catalyst (SAC) with porous N-doped carbon as the substrate. The catalyst exhibits a commercial Pt/C-comparable half-wave potential of 0.806 V (versus the reversible hydrogen electrode) in acid media with good stability. Furthermore, practical DMFCs test achieves a peak power density of over 200 mW cm−2 that far exceeds that of commercial Pt/C counterpart (82 mW cm−2). Particularly, the Mg−Co DMFC system runs over 10 h with negligible current loss under 10 M concentration methanol work condition. Experimental results and theoretical calculations reveal that the N atom coordinated by Mg and Co atom exhibits an unconventional d-band-ditto localized p-band and can promote the dissociation of the key intermediate *OOH into *O and *OH, which accounts for the near unity selective 4e− ORR reaction pathway and enhanced ORR activity. In contrast, the N atom in SACCo remains inert in the absorption and desorption of *OOH and *OH. This local coordination environment regulation strategy around active sites may promote rational design of high-performance and durable fuel cell cathode electrocatalysts.

Coordination-driven self-assembly of MOF-based heterostructures for electrocatalytic methanol oxidation

Direct methanol fuel cells (DMFCs) are considered one of the most promising energy conversion devices due to their environmentally friendly and high-energy density features. However, the sluggish anode kinetics of the methanol oxidation reaction (MOR) acts as a bottleneck in the DMFCs system. Herein, a series of MOF-based heterogeneous electrocatalysts (NiWO4/MOF-74-x, Ni3V2O8/MOF-74-x) is constructed via a coordination-driven self-assembly strategy to enhance the catalytic property of the MOR. The heterogeneous interface between MOF-74 and Ni compounds is built by the Ni–O coordination interaction, which provides fast charge transfer and mass diffusion efficiency. Therefore, the optimal catalyst NiWO4/MOF-74 (3) exhibits excellent MOR activity and operation durability with a peak current density of 28.58 ​mA·cm-2. This work is expected to inspire the design of more efficient MOF-based heterogeneous electrocatalysts for MOR and other energy conversion applications.

Model-based observer for direct methanol fuel cell concentration estimation by using second-order sliding-mode algorithm

Accurate estimation of the real-time methanol concentration of direct methanol fuel cell (DMFC) stack is a key technique for its feedback control and optimization. However, existing data-based methods as well as voltage fluctuation methods require a large amount of data to estimate methanol concentration, which increases the burden of embedded systems. What needs to be concerned is the methanol concentration inside the stack, because it directly affects its output power, while the existing research pay more attention to the methanol supplied concentration. To this end, a model-based observer based on second-order sliding-mode (SOSM) algorithm, is proposed to estimate the real-time methanol concentration inside DMFC stack utilizing the easily measured signals, such as DMFC stack voltage, current, and temperature. To validate the proposed method, the simulation comparisons between proposed SOSM observer and existing first-order sliding-mode (FOSM), extend Kalman filter (EKF) observer were carried out under certain operation conditions. Further, experimental verifications were implemented by using a real commercial DMFC system data to verify the performance of proposed approach. The comprehensive results demonstrates that proposed SOSM observer could estimate DMFC methanal concentration with robustness and accuracy.

Recent Advances in the Development of Nanocatalysts for Direct Methanol Fuel Cells

Direct methanol fuel cells (DMFCs) have attracted much attention due to their potential application as a power source for portable devices. Their simple construction and operation, associated with compact design, high energy density, and relatively high energy-conversion efficiency, give the DMFCs an advantage over other promising energy production technologies in terms of portability. Nowadays, research on DMFCs has received increased attention in both academics and industries. However, many challenges remain before these systems become commercial, including their costs and durability. As a key material with a high-value cost, noble metal catalysts for both the anode and cathode sides face several problems, which hinder the commercialisation of DMFCs. This paper provides a detailed comprehensive review of recent progress in the development of nanocatalysts (NCs) for the anode and cathode reactions of DMFCs, based on Platinum, Platinum-hybrid, and Platinum-free materials. Particular attention is devoted to the systematisation of published experimental results tested in DMFC devices since 2015, with an emphasis on passive DMFC systems. In addition, a dedicated section was created to include modelling/theoretical studies. Some open problems and remaining challenges are also highlighted in the final section.

Direct methanol fuel cells system–A review of dual-role electrocatalysts for oxygen reduction and methanol oxidation

One fundamental challenge in exploiting direct methanol fuel cells (DMFCs) is the preparation of inexpensive, high active electrocatalysts, which are highly active and durable for the two half-reactions, i.e., the methanol oxidation reaction (MOR) at the anode and the oxygen reduction reaction (ORR) at the cathode. Platinum group metals-based catalysts have been known the governing dual-functional electrocatalysts based on the literature reports. But these catalysts are expensive and commercialize the DMFC less attractive. In addition to the high-cost, there are also methanol crossover, CO poisoning, long-term instability, and other problems as for Pt-based spurs. For the dual-role MOR & ORR catalysts, methanol crossover is inevitable to a certain extent on the current development of DMFC with losses in terms of cell voltage. In this regard, one strategy is to exploit high selective anodic/cathodic electrocatalysts to capitalize the energy density at a high concentration of methanol. According to the summary results, there are mainly two types of dual-role electrocatalysts: one is Pt-support/co-catalyst (designated as P-S/C) for MOR/ORR, the other is catalyst/co-catalyst (designated as C/C) for MOR/ORR. This paper aims to review the design and construction of the various dual-role catalysts and give some discussion briefly.

Phosphate-decorated Pt Nanoparticles as Methanol-tolerant Oxygen Reduction Electrocatalyst for Direct Methanol Fuel Cells

In a direct methanol fuel cell system (DMFC), one of the drawbacks is methanol crossover. Methanol from the anode passes through the membrane and enters the cathode, causing mixed potential in the cell. Only Pt-based catalysts are capable of operating as cathode for oxygen reduction reaction (ORR) in a harsh acidic condition of DMFC. However, it causes mixed potential due to high activity toward methanol oxidation reaction of Pt. To overcome this situation, developing Pt-based catalyst that has methanol tolerance is significant, by controlling reactant adsorption or reaction kinetics. Pt/C decorated with phosphate ion was prepared by modified polyol method as cathode catalyst in DMFC. Phosphate ions, bonded to the carbon of Pt/C, surround free Pt surface and block only methanol adsorption on Pt, not oxygen. It leads to the suppression of methanol oxidation in an oxygen atmosphere, resulting in high DMFC performance compared to pristine Pt/C.

Methanol Sensor-Less Control Strategy for Direct Methanol Fuel Cell Startup

It is critical and challenging to start direct methanol fuel cells (DMFCs) from various environmental states to an ideal operating state by a sensor-less method. This paper presents a novel methanol sensor-less startup control (SLSC) algorithm based on the unimodal relationship of current vs. methanol concentration at a constant cell voltage during DMFC startup. A series of experiments indicate that the SLSC algorithm is capable of starting a DMFC under various initial concentrations and initial temperatures and can be easily adjusted to reduce the startup time or improve the energy efficiency. The wide applicability and easy adjustment characteristics give the SLSC algorithm a potential prospect in the DMFC system.

Local entropy generation and exergy analysis of the condenser in a direct methanol fuel cell system

This paper aims to identify the irreversibilities in the condenser of a direct methanol fuel cell (DMFC) system and present possible enhancements in its design through local entropy generation analysis (L-EGA). For this purpose, the local entropy generation terms originating from heat and mass calculated from results of a pseudo two-phase computational fluid dynamic (CFD) model of the condenser. Through this analysis, the total irreversibilities due to heat and mass transfer are calculated locally (e.g., film boundary layer, vapour-gas boundary layer) under the variable operating conditions of a DMFC (undersaturated, saturated, and supersaturated conditions of the cathode exhaust gas). Moreover, the exergy destruction ratio of condenser is found to estimate the exergy performance of the condenser. The results show that in the case of supersaturated cathode exhaust gas (CEG) flow, the entropy generation rate due to mass transfer in the film region is found as 0.032 W/(m·K) which is 18 times higher than that for the undersaturated CEG flow. However, entropy generation rate due to mass transfer decreases significantly when the hot flow is just over the film region. In the film region, the entropy generation rates originating from heat transfer are found as 0.0055 W/(m·K) (for the undersaturated case), 0.0032 W/(m·K) (for the saturated case), and 0.0015 W/(m·K) (for the supersaturated case). Moreover, the maximum exergy destruction ratio is found as 0.72 when the CEG is undersaturated and the CEG velocity is 0.18 m/s, while the lowest exergy destruction ratio is calculated as 0.28 when the CEG is saturated.

Determination of component drags coefficients in direct methanol fuel cell

Direct Methanol Fuel Cell (DMFC) system is considered as one of the most important clean and sustainable energy generation system. This system generates energy by electro oxidization of methanol however, this reaction is not fully completed. Consequently, the efficiency of the system is lower than expected. Studies in literature generally assume a fully completed methanol electrooxidation reaction (MOR) however, since MOR is not fully completed in this system. Thus, it is significant to consider the reaction intermediates. Therefore, this study focused on evaluating some critical parameters such as diffusion coefficients, component drag coefficients, and activation energies by considering reaction intermediates forms from MOR at the operating conditions. According to the experimental data, the properties of electroosmotically dragged substances in an operating DMFC system were investigated. First, the polarization curve was obtained, and then the system was run at constant current density for mid-term experiments. Next, the effect of the changes in DMFC operating conditions on performance was examined. Accordingly, component drag coefficients at 55 °C for methanol and water were obtained as 0.000246 and 3.1, respectively.

Modeling the Output Power of Direct Methanol Fuel Cells Using SVR

The output power of Direct Methanol Fuel Cells (DMFC) is one of the most important elements which limit the performance of DMFC. In order to enhance performance of DMFC, it is necessary to have model to modeling the output power of DMFC. In this paper, a novel model base on Support Vector Regression (SVR) to modeling the output power of DMFC base on output current (I) and operating temperature (T). The test result is shown that the generalization ability of SVR model is high accuracy. This investigation suggests that SVR is quite satisfied used to developing a DMFC model and can be used for controlling, optimal designing and feasibility study of the DMFC system.

A robust methanol concentration sensing technique in direct methanol fuel cells and stacks using cell dynamics

The electrochemical behaviour of direct methanol fuel cells (DMFCs) is sensitive to methanol concentration; thus, to avoid external sensors, it is a promising candidate to monitor the concentration of methanol in the fuel circulation loop, which is central to the efficient operation of direct methanol fuel cell systems. We address this issue and report on an extremely robust electrochemical methanol sensing technique that is not sensitive to temperature, cell degradation and membrane electrode assembly (MEA) type. We develop a temperature independent empirical correlation of the dynamic response of cell voltage to step changes in current with methanol concentration. This equation is successfully validated under various operating scenarios at both the single cell and stack levels. Our sensing method achieves an impressive accuracy of ±0.1 M and this is expected to increase the reliability of methanol sensing and simplify the control logic of DMFC systems.

Optimization and control of fuel cell thermal management system based on neural network

Aiming at the direct methanol fuel cell system is too complicated, difficult to model, and the thermal management system needs to be optimized. The article attempts to bypass the internal complexity of direct methanol fuel cell, based on experimental data, use neural networks to approximate arbitrarily complex non-linear functions ability to apply neural network identification methods to direct methanol fuel cell, a highly non-linear thermal management system optimization modelling. The paper uses 1000 sets of battery voltage and current density experimental data as training samples and uses an improved back propagation neural network to establish a battery voltage-current density dynamic response model at different temperatures. The simulation results show that this method is feasible, and the established model has high accuracy. It makes it possible to design the real-time controller of the direct methanol fuel cell and optimize the thermal energy manage?ment system?s efficiency.

Constructing a graphene-contained layer in anode to improve the performance of direct methanol fuel cells using high-concentration fuel

ABSTRACT A novel membrane-electrode structure is conceived and prepared in this work, where a graphene-contained layer is constructed between anode catalyst layer and membrane, also the material composition in this layer is optimized to improve the performance of a direct methanol fuel cell (DMFC) with high-concentration fuel. The polarization test shows that the pristine graphene layer could reduce the methanol crossover, while causing a slight decrease in performance. After adding Nafion ionomer binder in the graphene layer, the peak power density of the electrode fed with 8 M methanol reaches 17.75 mW cm−2, which is increased by 12.36% and 82.69% compared with the conventional electrode and the electrode without any binder in the graphene layer, respectively. Electrochemical impedance spectroscopy (EIS) and cyclic voltammetry (CV) results show that for the graphene-contained layer including Nafion ionomer binder, the charge transfer resistance is only one-fifth of that without binder in the graphene layer, and the anode electrochemical active surface area (ECSA) is increased by 40.16%. These results indicate that the anode electrode with a graphene-contained layer using Nafion ionomer as the binder can effectively improve the cell performance with high-concentration fuel, which is beneficial to increase the energy density of a DMFC system.

Joint operation of adaptive numerical simulation and adaptive optimization for direct methanol fuel cell performance improvement

Abstract A joint operation method is proposed in this study for collaborative design of multi-type parameters in direct methanol fuel cell system. This method consists of adaptive numerical simulation for fuel cell operation and adaptive optimal design of the fuel cell system. The simulation key coefficients are designed to be changed following the multi-type parameters variations in order to achieve adaptive numerical simulation. An efficient optimization method surrogate-assisted meta-heuristic optimization algorithm is designed for adaptive optimal design. The data transmission would be realized between optimal design method and simulation process to serve for the joint operation process. The results show that adaptive numerical simulation could guarantee the simulation accuracy under different values of multi-type parameters. Meanwhile, the joint operation could significantly improve the efficiency for optimal design of parameters in DMFC system. Furthermore, the performance improvement has been validated by experiments with a 7.32% increment of energy conversion performance.