1. Introduction

Hydrogen energy is the most dynamic and promising form of sustainable energy. It serves as an ideal alternative to conventional fossil fuels. Currently, hydrogen fuel cells, which utilize hydrogen as an energy source, have a wide range of promising applications in transportation. However, there are some challenges associated with the storage and supply of hydrogen. On-board hydrogen production from liquid hydrocarbon sources becomes an effective solution. Methanol, as one of the carriers of hydrogen, has the advantages of high energy density, abundant sources, a low boiling point, a high hydrogen/carbon ratio, absence of C–C bonds, renewability, and environmental friendliness. MSR is particularly important for hydrogen production, which exhibits relatively moderate reaction temperatures, high yields of hydrogen, and low levels of impurities. However, hydrogen production from MSR in vehicles still faces some challenges, one of which is that it takes too long to achieve instant hydrogen production during cold starts.

The ability to rapidly cold start an on-board methanol-to-hydrogen fuel cell means that it may be possible to achieve a timely hydrogen supply, and the generation of harmful gases during the cold start process can be reduced. Uniform heating performance can ensure the efficiency of the catalyst and extend its lifespan for endothermic reactions. At present, the primary heat sources for the MSR are traditional resistance heating (RH) and fuel heating (FH), and significant achievements have been made on this basis. However, RH, which heats the material from the outer surface inward, is plagued by slow heating rates and uneven temperature distribution. Fuel heating requires additional combustion control systems, and the separation between the combustion exhaust gas and the hydrogen production unit also presents a challenge. Currently, studies are also being conducted on the use of microwave and plasma heating catalytic MSR for hydrogen production. Both microwave heating and plasma heating achieve non-contact heating, which results in a significant reduction in heat loss and energy consumption. However, control of heating temperature is challenging, and the heating rate is relatively low, which limits its practical application.

EIH is a technology that utilizes high-frequency electromagnetic fields to induce eddy currents and generate Joule heat in conductors, thereby facilitating the heating of objects. Due to its high efficiency and energy conservation, precise temperature regulation, rapid heating rate, eco-friendliness, EIH has been widely applied in metallurgy, drug delivery systems, magnetic hyperthermia therapy, and synthesis reactions, among other areas. However, only a few studies have adopted EIH with high Curie temperature, such as Iron, nickel, and cobalt, by combining with catalysts. Wu et al. improved biomass steam gasification hydrogen production by combining the constructed Ni–CaO–C catalyst with the induction heating technology. Varsano et al. employed a magnetic induction-driven nickel-cobalt alloy as a catalyst for methane dry reforming, which resulted in high methanol conversion and hydrogen yield. By combining the methanol steam reforming reaction with electromagnetic induction heating technology, Guan et al. proposed a catalyst-coated tube reactor for applications such as vehicle hydrogen sources or distributed hydrogen energy. However, due to the smooth surface and low specific surface area, the catalyst loading rate of the metal support is low and susceptible to detachment. To enhance the methanol conversion rate and H₂ yield, Zhou et al. employed a porous metal fiber sintered felt with a high specific surface area as the catalyst support. However, the felt exhibits inadequate thermal stability. Therefore, integrating porous magnetic materials with high catalyst loading, superior loading strength, elevated Curie temperature, excellent stability, and an efficient EIH system is expected to introduce new opportunities in the field of catalysis.

In fact, besides metal materials like iron, cobalt, nickel, and alloy materials such as iron chromium cobalt and aluminum nickel cobalt with high Curie temperatures, some ferrites also possess a high Curie temperature. For instance, NiFe₂O₄ has a Curie temperature of 580 °C and a maximum operating temperature of 486 °C. In this investigation, the porous magnetic ferrites are expected to be used as catalyst supports for catalytic reactions. NiFe₂O₄ porous ceramic with high specific surface area and high Curie temperature will be fabricated using 3D-printing technology and used as the catalyst support. The performance of rapid heating by EIH and hydrogen production of MSR based on NiFe₂O₄ porous ceramic will also be evaluated. Additionally, traditional RH for MSR based on general cordierite support will be conducted for comparison.

2. Experimental

2.1. Preparation and pretreatment of porous ceramic

2.1.1. Synthesis of NiFe₂O₄ powder and preparation of NiFe₂O₄ porous ceramic

Firstly, NiFe₂O₄ powder was synthesized using Fe₂O₃ powder and NiO powder through the solid-state reaction. The Fe₂O₃ powder (purity ≥99%, 5 μm) and NiO powder (purity ≥99.8%, 10 μm) were purchased from Hebei Qinghe Xinhu Metal Materials Co., Ltd. The Fe₂O₃ powder and NiO powder were ball-milled at a 1:1 M ratio for 8 h until they were thoroughly mixed and refined. Then, the mixture was calcined in a muffle furnace at 1000 °C for 2 h to synthesize NiFe₂O₄ through the solid-state reaction. After that, the synthesized NiFe₂O₄ powder was prepared by sieving.

The second step involves preparing a honeycomb porous NiFe₂O₄ ceramic using 3D printing. The NiFe₂O₄ powder, PVA solution (5 wt%, Sinopharm Chemical Reagent Co., Ltd., DP = 1750 ± 50), polymethyl methacrylate (PMMA, Dongguan Tesulang Co., Ltd., D50 = 60 μm), and deionized water were mixed in a mass ratio of 100:40:3:15 to form a slurry. Then, a honeycomb green body was produced by a Direct Ink Writing 3D printer (STSW-5060, Hunan ShuTao 3D Technology Co., Ltd.). After being dried, the printed body was sintered in an air atmosphere at 1100–1200 °C for 2 h to obtain a cylindrical NiFe₂O₄ porous ceramic with a diameter of 30 mm and a height of 10 mm. The specific process is shown in Fig. 1.