Development of highly efficient methanol steam reforming system for hydrogen production and supply for a low temperature proton exchange membrane fuel cell

Methanol steam reforming (MSR) has been regarded as a promising hydrogen supply method for proton exchange membrane fuel cell (PEMFC), while the efficiency for hydrogen production and integration method of MSR with PEMFC are two major challenges for commercial applications. Here, we present a highly efficient MSR system for hydrogen production and supply for low temperature PEMFC (LT-PEMFC). The MSR system has a highly compact microreactor, wherein MSR, methanol combustion, and CO selective methanation reactions occur. The CO selective methanation is used to reduce the content of CO concentration to remit the CO poison, then the reformate of MSR system is mixed with air and supply for the LT-PEMFC. Then, experimental tests are conducted to investigate the effects of operating parameters on hydrogen production. A staged supply strategy is proposed, it enables to startup the system within 11.2 min and with methanol consumption of 34.72 g. Results show that the methanol conversion can reach up to 93.0% and system's energy efficiency of 76.2%. After integration with a LT-PEMFC, a maximum 160 W electricity can be generated. The results obtained in this study demonstrated that the developed MSR system can be used to supply hydrogen for LT-PEMFC and able to power mobile device requiring hundreds of watts power consumption.     

Hydrogen production in microreactor using porous SiC ceramic with a pore-in-pore hierarchical structure as catalyst support

Porous SiC ceramic as catalyst support with porous CuO/ZnO/CeO₂/ZrO₂ catalyst was fabricated via solution combustion method and used in a microreactor. A pore-in-pore hierarchical structure was formed on the support by using glycol as the fuel. The effects of fuel/nitrates molar ratio on the particle size, residual carbon, reducibility and structure of catalyst on the support were investigated. The optimal content of glycol was proposed and the catalytic performance of microreactor was further studied. Results showed that the catalyst loading amount was about 20% weight of the whole support and the loading intensity was strong. Moreover, the microreactor achieved a 100% methanol conversion rate at 280 °C and the conversion rate stayed around 95% after 30 h reaction by using the support over the optimal content of glycol, which exhibited excellent superiority in the methanol steam reforming process.     

Fabrication of high aspect ratio ceramic micro-channel in diamond wire sawing as catalyst support used in micro-reactor for hydrogen production

Ceramic is an ideal material for preparing micro-channel catalyst supports with their characteristics of high temperature resistance, corrosion resistance and mechanical strength. High aspect ratio micro-channel structure has the advantages of large specific surface area, strong mass and heat transfer performance and high material utilization. However, ceramic materials are hard and brittle, and it is difficult to fabricate micro-channel structures with aspect ratio more than 1.5:1 by traditional processing methods. In this paper, a cutting method of large diameter diamond wire sawing was proposed. The micro-channels with width of 520 μm and aspect ratio of more than 4:1 was successfully fabricated by this method. Furthermore, the integrity of the micro-channel structure processed by diamond wire sawing was analyzed. And than the effect of surface morphology in different processing parameters on the catalyst loading performance were studied. The catalyst loading strength of ceramic slices with different surface morphology was tested. Finally, the ceramic micro-channel array was used as the catalyst support in micro-reactor for hydrogen production via methanol steam reforming (MSR). The methanol conversion rate and H₂ production rate could reach 87.8% and 74.6 mmol/h, respectively under GHSV 12600 ml/g·h at 300 °C. The experimental results show that the large-diameter diamond wire sawing technology can be used to process ceramic microchannels with high aspect ratio; using ceramic microchannel arrays as catalyst supports in hydrogen production can obtain better reaction performance; the feasibility of ceramic materials were broadened as microchannel catalyst supports.     

Feasibility of preparing additive manufactured porous stainless steel felts with mathematical micro pore structure as novel catalyst support for hydrogen production via methanol steam reforming

In this paper, an additive manufacturing prepared porous stainless steel felt (AM-PSSF) is proposed as a novel catalyst support for hydrogen production via methanol steam reforming (MSR). In the method, 316 L stainless steel powder with diameter of 15–63 μm is processed by the additive manufacturing technology of selective laser melting (SLM). To accomplish the preparation, the reforming chamber where the AM-PSSF is embedded is firstly divided into an all-hexahedron mesh. Then, the triply periodic minimal surface (TPMS) unit with mathematical form, high interconnectivity and large specific surface area is mapped into the hexahedrons based on shape function, forming the fully connected three-dimensional (3D) micro pore structure of the AM-PSSF. By correlating the mathematical parameter and the porosity of the TPMS unit, and taking into account the SLM process, the porosity of the AM-PSSF is well controlled. Based on the designed 3D pore structure model, the AM-PSSF is produced using standard SLM process. The application of the AM-PSSF as catalyst support for hydrogen production through MSR indicates that: 1) both the naked and catalyst-coated AM-PSSF have the characteristics of high porosity, large specific surface area and high connectivity; 2) the MSR hydrogen production performance of the AM-PSSF is better than that of the commercial stainless steel fiber sintered felt. The feasibility of AM-PSSF as catalyst support for MSR hydrogen production may pave a better way to balance different requirements for catalyst support, thanks to the excellent controllability provided by AM on both the external shape and the internal pore structure, and to the produced rough surface morphology that benefits the catalyst adhesion strength. In addition, catalyst support with pore structures that are more accommodated with the flow field and the reaction rate of MSR reaction may be prepared in future, since the entire catalyst support structure, from macro scale to micro scale, is under control.     

Hydrogen generation from sodium borohydride using microreactor for micro fuel cells

A microreactor for hydrogen generation from sodium borohydride was designed and fabricated in the present study. The microreactor has three photosensitive glasses, including the cover, the reactor layer and the base. A nickel form was inserted in the reactor layer as a catalyst support. A Co-P-B catalyst for sodium borohydride hydrolysis was coated on the nickel form by electroless plating. The characteristics of the catalyst were studied using SEM and EDS analysis. The hydrogen generation rate of the microreactor was measured under a variety of conditions and made up 15.6 ml/min at a temperature of 40 °C. The generated hydrogen was supplied to a micro fuel cell with a maximum power output of 157 mW at a current of 0.5 A.     

Catalytic performance of a high-cell-density Ni honeycomb catalyst for methane steam reforming

The catalysis of methane steam reforming (MSR) by pure Ni honeycombs with high cell density of 2300 cells per square inch (cpsi) was investigated to develop efficient and inexpensive catalysts for hydrogen production. The Ni honeycomb catalyst was assembled using 30-μm-thick Ni foils, and showed much higher activity than that of a Ni honeycomb catalyst with cell density of 700 cpsi at a steam-to-carbon ratio of 1.36 and a gas hourly space velocity of 6400 h^?1 in a temperature range of 873–1173 K. Notably, the activity increased approximately proportional to the increasing geometric specific surface area of the honeycombs. The turnover rate of the Ni honeycomb catalyst was higher than that of supported Ni catalysts. The changes in chemical state of the Ni catalyst during hydrogen reduction and MSR reaction were analyzed by in situ X-ray absorption fine structure spectroscopy, which revealed that deactivation was mainly due to oxidation of the surface Ni atoms. These results demonstrated that the high-cell-density Ni honeycomb catalyst exhibits good performance for MSR reaction, and easy regeneration of the deactivated Ni honeycomb catalyst is possible only via hydrogen reduction.     

Production of hydrogen from methanol steam reforming using CuPd/ZrO2 catalysts – Influence of the catalytic surface on methanol conversion and CO selectivity

Electricity generation for mobile applications by proton exchange membrane fuel cells (PEMFCs) is typically hindered by the low volumetric energy density of hydrogen. Nevertheless, nearly pure hydrogen can be generated in-situ from methanol steam reforming (MSR), with Cu-based catalysts being the most common MSR catalysts. Cu-based catalysts display high catalytic performance, even at low temperatures (ca. 250 °C), but are easily deactivated. On the other hand, Pd-based catalysts are very stable but show poor MSR selectivity, producing high concentrations of CO as by-product. This work studies bimetallic catalysts where Cu was added as a promoter to increase MSR selectivity of Pd. Specifically, the surface composition was tuned by different sequences of Cu and Pd impregnation on a monoclinic ZrO₂ support. Both methanol conversion and MSR selectivity were higher for the catalyst with a CuPd-rich surface compared to the catalyst with a Pd-rich surface. Characterization analysis indicate that the higher MSR selectivity results from a strong interaction between the two metals when Pd is impregnated first (likely an alloy). This sequence also resulted in better metallic dispersion on the support, leading to higher methanol conversion. A H₂ production rate of 86.3 mmol h^?1 g^?1 was achieved at low temperature (220 °C) for the best performing catalyst.     

Hydrogen production employing Cu/Zn-BTC metal-organic framework on cordierite honeycomb ceramic support in methanol steam reforming process within a microreactor

Three metal-organic frameworks Cu-BTC, Zn-BTC, and Cu/Zn-BTC were prepared and impregnated in nitrate solutions to obtain the precursors. After calcination, three metal-BTC-derived CuO/ZnO/CeO₂/ZrO₂ catalysts were obtained. The samples were characterized and the catalyst-coated cordierite honeycomb ceramics were used in a microreactor for methanol steam reforming at different reaction conditions. Results showed that the Cu/Zn-BTC-derived catalyst exhibited the most fine and uniform particles, the best reducibility, the largest specific surface area, and the optimal surface elemental state due to the difference in the formation mechanisms, resulting in its remarkable catalytic performance. The ceramic support coated with Cu/Zn-BTC-derived catalyst could achieve 100% methanol conversion rate and 0.336 mol/h H₂ output at 260 °C in the microreactor. Stability tests demonstrated that the Cu/Zn-BTC-derived catalyst could maintain its excellent performance without deactivation within 30 h continuous reaction, which was connected with the Ce–Zr–O solid solution with high concentration of oxygen vacancies and surface oxygen.     

Development of methanol steam reforming microreactor based on stacked wave sheets and copper foam for hydrogen production

Methanol steam reforming has been used for in-situ hydrogen production and supply for proton exchange membrane fuel cell (PEMFC), while its power density and energy efficiency still needs to be improved. Herein, we present a novel methanol steam reforming microreactor based on the stacked wave sheets and copper foam for highly efficient hydrogen production. The structural of stacked wave sheets and copper foam, and their roles in the microreactor are described, methanol catalytic combustion is adopted to supply heat for methanol steam reforming reaction and enables the microreactor to work automatically. For catalyst carrier, a fractal body-centered cubic model is established to study the flow characteristics and chemical reaction performances of the copper foam with coated catalyst layer. Both simulation and experimental results showed that the reformate flowrate increases with the increasing of microreactor layers and methanol solution flowrate, the discrepancies of methanol conversion between simulation and experimental tests are less than 7%. Experimental results demonstrated that the reformate flowrate of 1.0 SLM can be achieved with methanol conversion rate of 65%, the output power of the microreactor is 159 W and power density is 395 W/L. The results obtained in this study indicates that stacked wave sheets and copper foam can uniform the reactant flow and improve the hydrogen production performances.     

Structural design of self-thermal methanol steam reforming microreactor with porous combustion reaction support for hydrogen production

To replace the traditional electric heating mode and increase methanol steam reforming reaction performance in hydrogen production, methanol catalytic combustion was proposed as heat-supply mode for methanol steam reforming microreactor. In this study, the methanol catalytic combustion microreactor and self-thermal methanol steam reforming microreactor for hydrogen production were developed. Furthermore, the catalytic combustion reaction supports with different structures were designed. It was found that the developed self-thermal methanol steam reforming microreactor had better reaction performance. Compared with A-type, the △T_max of C-type porous reaction support was decreased by 24.4 °C under 1.3 mL/min methanol injection rate. Moreover, methanol conversion and H₂ flow rate of the self-thermal methanol steam reforming microreactor with C-type porous reaction support were increased by 15.2% under 10 mL/h methanol-water mixture injection rate and 340 °C self-thermal temperature. Meanwhile, the CO selectivity was decreased by 4.1%. This work provides a new structural design of the self-thermal methanol steam reforming microreactor for hydrogen production for the fuel cell.     

Numerical modeling of microchannel reactors with gradient porous surfaces for hydrogen production based on fractal geometry

A microchannel reactor with a porous surface catalyst support has been applied to methanol steam reforming (MSR) for hydrogen production. The fluid flow, heat transfer, and hydrogen production efficiency of the microchannel reactor are significantly affected by the fabricated porous surface support, such as the pore sizes and their distributions. This paper presents a novel microchannel reactor with a gradient porous surface as the reaction substrate to enhance the performance of the microreactor for hydrogen production. Numerical modeling of the gradient porous surface is developed based on fractal geometry, and three different types of porous surfaces as the catalyst supports (two gradient porous surfaces and one uniform pore-size surface) are investigated. The fluid flow and heat transfer characteristics of these three types of microchannel reactors are studied numerically, and the results showed that the microreactor with a positive gradient pore sized surface exhibited relatively better overall performance. Experimental setups and tests were performed and the results validate that the microchannel reactor with a positive gradient porous surface can increase the heat transfer performance by up to 18% and can decrease the pressure drop by up to 8% when compared to a microreactor with a uniform pore sized surface. Hydrogen production experiments demonstrated that the microreactor with positive gradient pore sizes has the highest methanol conversion rate of 56.3%, and this rate is determined to be 6% and 9% higher than that of microreactors with reverse gradient porous surfaces and uniform pore sized surface, respectively.     

One-step growth of CuO/ZnO/CeO2/ZrO2 nanoflowers catalyst by hydrothermal method on Al2O3 support for methanol steam reforming in a microreactor

CuO/ZnO/CeO₂/ZrO₂ nanoflowers catalyst was grown on an Al₂O₃ foam ceramic by a one-step hydrothermal process, while a naked Al₂O₃ foam ceramic and an Al₂O₃ foam ceramic grown with ZnO nanorods that directly impregnated into the catalyst precursor solution were also fabricated simultaneously. The morphology, composition, redox property and specific surface area of catalysts on the three ceramics were investigated in detail. The catalyst-loaded ceramics were used as catalyst supports in a microreactor to study the catalytic performance for methanol steam reforming. Results showed that the microreactor with Al₂O₃ support grown with nanoflowers catalyst achieved 99.8% methanol conversion rate, 0.16 mol/h H₂ flow rate at 310 °C, and an inlet methanol flow rate of 0.048 mol/h. Moreover, the microreactor exhibited 92% methanol conversion rate after 30 h continuous reaction.     

Methanol steam reforming microreactor with novel 3D-Printed porous stainless steel support as catalyst support

In order to study the methanol steam reforming performance of the 3D-printed porous support for hydrogen production, three dimensional (3D) printing technology was proposed to fabricate porous stainless steel supports with body-centered cubic structure (BCCS) and face-centered cubic structure (FCCS). Catalyst loading strength of the 3D-printed porous stainless steel supports was studied. Moreover, methanol steam reforming performance of different 3D-printed porous supports for hydrogen production was experimentally investigated by changing reaction parameters. The results show that the 3D-printed porous stainless steel supports with BCCS and FCCS exhibit better catalyst loading strength, and can be used in the microreactor for methanol steam reforming for hydrogen production. Compared with 90 pores per inch (PPI) Fe-based foam support, 3D-printed porous stainless steel supports with FCCS and BCCS show the similar methanol steam reforming performance for hydrogen production in the condition of 6500 mL/(g·h) gas hourly space velocity (GHSV) with 360 °C reaction temperature. This work provides a new idea for the structural design and fabrication of the porous support for methanol steam reforming microreactor for hydrogen production.     

Development of a microreactor for the production of hydrogen from ammonia

This paper describes the development of a structured aluminum-anodized alumina microreactor that exhibits high catalytic activity for the decomposition of anhydrous ammonia to nitrogen and hydrogen at moderate temperatures. Modifications such as adjustments to the geometry of the microreactor features, surface area enhancement of the anodized catalyst support, choice of Ru precursor, and application of a catalyst promoter are each shown to affect the reactor performance to varying degrees. The reactor converts 99% of ammonia at 600 °C into the equivalent of 60 W of hydrogen. These numbers are sufficient for to merit serious consideration for use in practical applications, particularly in mobile devices fueled by hydrogen where monolithic structures are advantageous.     

Impact of Ni-based catalyst patterning on hydrogen production from MSR: External steam reformer modelling

Wall-coated Methane Steam Reformers (MSR) are commonly used as fuel processing in the hydrogen production chain. In such devices, the catalyst which is generally nickel-based is coated on the walls, and the heat supply influences directly the fuel processing efficiency. In this work, two-dimensional CFD study is carried out to explore an enhancement on MSR thermal behavior. Two configurations in terms of catalyst coating are investigated. The first MSR configuration is equipped with continuous catalytic layer, while in the second, discrete catalyst layers separated by an inert gap are imposed. The effect of the catalyst patterning on the thermal and mass behavior of MSR is discussed. The results show that the MSR efficiency can be improved by extending the catalytic zone and discretizing the catalyst coating. Comparing to conventional MSR with continuous catalytic layers, enhancement of 28.71% in CH₄ conversion and 88.574% in H₂ production is realized by using discretized catalytic layers.     

Porous copper fiber sintered felts with surface microchannels for methanol steam reforming microreactor for hydrogen production

In this study, a laser micro-milling technique was introduced into the fabrication process of surface microchannels with different geometries and dimensions on the porous copper fiber sintered felts (PCFSFs). The PCFSFs with surface microchannels as catalyst supports were then used to construct a new type of laminated methanol steam reforming microreactor for hydrogen production. The microstructure morphology, pressure drop, velocity and permeability of PCFSF with surface microchannels were studied. The effect of surface microchannel shape (rectangular, stepped, and polyline) and catalyst loading amount on the reaction performance of methanol steam reforming microreactor for hydrogen production was further investigated. Our results show that the PCFSF with rectangular microchannels demonstrated a lower pressure drop, higher average velocity and higher permeability compared to the stepped and polyline microchannel. Furthermore, the PCFSF with rectangular microchannels also exhibited the highest methanol conversion and H₂ flow rate. The best reaction performance of methanol steam reforming microreactor for hydrogen production was obtained using PCFSF with rectangular microchannels when 0.5 g catalyst was loaded.     

Numerical and experimental study on hydrogen production via dimethyl ether steam reforming

This work presents the characteristics of catalytic dimethyl ether (DME)/steam reforming based on a Cu–Zn/γ-Al₂O₃ catalyst for hydrogen production. A kinetic model for a reformer that operates at low temperature (200 °C–500 °C) is simulated using COMSOL 5.2 software. Experimental verification is performed to examine the critical parameters for the reforming process. During the experiment, superior Cu–Zn/γ-Al₂O₃catalysts are manufactured using the sol-gel method, and ceramic honeycombs coated with this catalyst (1.77 g on each honeycomb, five honeycombs in the reactor) are utilized as catalyst bed in the reformer to enhance performance. The steam, DME mass ratio is stabilized at 3:1 using a mass flow controller (MFC) and a generator. The hydrogen production rate can be significantly affected depending on the reactant's mass flow rate and temperature. And the maximum hydrogen yield can reach 90% at 400 °C. Maximum 8% error for the hydrogen yield is achieved between modeling and experimental results. These experiments can be further explored for directly feeding hydrogen to proton exchange membrane fuel cell (PEMFC) under the load variations.     

Hydrogen production via catalytic pulsed plasma conversion of methane: Effect of Ni–K2O/Al2O3 loading,applied voltage,and argon flow rate

Despite industrial application of methane as an energy source and raw material for chemical manufacturing, it is a potent heat absorber and a strong greenhouse gas. Evidently reduction of methane emission especially in the natural gas sector is essential. Methane to hydrogen conversion through non-thermal plasma technologies has received increasing attention. In this paper, catalytic methane conversion into hydrogen is experimentally studied via nano-second pulsed DBD plasma reactor. The effect of carrier gas flow, applied voltage, and commercial Ni–K₂O/Al₂O₃ catalyst loading on methane conversion, hydrogen production, hydrogen selectivity, discharge power, and energy efficiency are studied. The results showed that in the plasma alone system, the highest methane conversion and hydrogen production occurs at argon flow rate of 70 mL/min. Increase in the applied voltage increases the methane conversion and hydrogen production while it decreases the energy efficiency. Presence of 1 g Ni–K₂O/Al₂O₃ catalyst shifts the optimum voltage for methane conversion and hydrogen production to 8 kV, reduces the required power, and increases the energy efficiency of the process. Finally in the catalytic plasma mode the optimum process condition occurs at the argon flow rate of 70 mL/min, applied voltage of 8 kV, and catalyst loading of 6 g. Compared with the optimum condition in the absence of catalyst, presence of 6 g Ni–K₂O/Al₂O₃ catalyst increased the methane conversion, hydrogen production, hydrogen selectivity and energy efficiency by 15.7, 22.5, 7.1, and 40% respectively.     

Novel micro-channel methane reformer assisted combustion reaction for hydrogen production

A metal catalyst-containing, 80 ml, micro-channel reactor (MCR) with a section dedicated to combustion reaction was investigated for the potential application of on-board methane steam reforming (MSR) to hydrogen production. The metal catalyst was introduced into the MCR as a shape of a thin plate that was diffusion-bonded with the other micro-channel plates. The combustion reaction was performed on the other side of the MCR for direct provision of the necessary heat for the endothermic MSR and for miniaturizing the system volume. In the MCR, both the methane conversion and the hydrogen production rate are extremely high compared with those of the equilibrium under atmospheric pressure. The required heat of reaction is successfully provided by the combustion of either hydrogen or the methane mixture on the other side of the MCR without the need for any heating cartridges. This novel micro-channel reformer is suitable for application as a compact fuel processor due to its production of hydrogen-rich syn-gas, small volume, simple catalyst loading and use of an active and easily stackable catalyst.     

Enhancement of pure hydrogen production through the use of a membrane reactor

Pure hydrogen production is of great interest as it is an energy carrier which can be used in PEM fuel cells for power production. Methane Steam Reforming (MSR) is commonly used for hydrogen production although the produced hydrogen is not free of other components. Membrane Reactors (MR) enable a pure hydrogen product stream and allows the reaction to take place at significantly lower temperatures (lower than 550 °C) than in conventional reactors (greater than 800 °C) with comparable methane conversion. This is achieved by hydrogen removal through a permselective Pd–Ag based membrane that cause a favorable shift in chemical equilibrium towards hydrogen production. In the present study, a two-dimensional, nonlinear, and pseudo-homogeneous mathematical model of a catalytic fixed-bed membrane reactor for methane steam reforming over a nickel-based foam supported catalyst is presented. Simulated results referring to the distribution of species, methane conversion, temperature and hydrogen flowrate along the reactor for different radial positions are obtained and analyzed. The performance of structured catalyst and catalyst supported on foam configurations under the same operating conditions is also studied. Experimental results for the membrane facilitate the identification of suitable operating conditions.