Joule Heating: An Emerging Strategy for Ultrafast Catalyst Synthesis
Abstract
Catalyst development lies at the core of advanced energy conversion, environmental remediation and chemical synthesis technologies. Traditional catalyst fabrication methods, including conventional tube furnace calcination, hydrothermal reaction and sol-gel method, generally suffer from prolonged reaction duration, high energy consumption, cumbersome operation procedures and uncontrollable material microstructure. As an innovative ultrafast thermal processing technology, Joule heating has attracted extensive research attention in the field of rapid catalyst synthesis in recent years. This technique generates uniform and instantaneous high temperature inside conductive precursors via resistive thermal effect under electric excitation, realizing the high-efficiency preparation of high-performance catalysts within seconds to minutes. Compared with conventional thermal treatment strategies, Joule heating features ultra-fast heating/cooling rate, low energy loss, precise temperature regulation and excellent scalability, and exhibits unique advantages in constructing metastable phases, atomically dispersed active sites and high-entropy composite structures. This paper systematically elaborates the working principle of Joule heating technology, summarizes its prominent merits for catalyst synthesis, reviews its latest research progress in preparing diversified functional catalysts, and analyzes the current technical bottlenecks as well as future development directions, aiming to provide valuable references for the further optimization and industrialization of Joule heating-based catalyst synthesis.
1. Introduction
Against the backdrop of global carbon neutrality initiatives, green energy technologies such as water electrolysis, fuel cells, carbon dioxide reduction and nitrogen fixation have become research hotspots across the world, where high-efficiency and durable catalysts serve as the decisive factor restricting the overall performance of related energy devices . The microscopic morphology, crystal phase structure, electronic distribution and active site dispersion of catalysts are directly determined by synthesis conditions. Traditional thermal synthesis approaches rely on external radiation heat transfer to heat raw materials, which inevitably leads to slow temperature rise, uneven heat distribution and long annealing cycles (usually several hours). The prolonged high-temperature environment often triggers the agglomeration of active nanoparticles, the collapse of carrier structures and the loss of high-activity metastable phases, severely limiting the performance improvement of catalysts .
To break through the limitations of conventional heating modes, researchers have explored a variety of emerging rapid thermal processing technologies. Among them, Joule heating, also known as flash Joule heating (FJH), stands out due to its distinctive internal heating mechanism and outstanding comprehensive performance. Different from external heating methods, Joule heating directly converts electric energy into thermal energy inside conductive substrates or precursor materials through resistance effect, achieving an ultra-high heating rate up to 10–10 °C/s and a maximum transient temperature exceeding 3000 K . Benefiting from the ultra-short high-temperature action time, this technology can complete precursor crystallization, phase transformation and heteroatom doping in an extremely short period, while inhibiting the adverse structural evolution caused by long-term high-temperature treatment. At present, Joule heating has been successfully applied to the rapid synthesis of single-atom catalysts, alloy catalysts, carbon-based composite catalysts and metal oxide catalysts, covering almost all mainstream catalytic reaction systems.
2. Fundamental Principle of Joule Heating
The basic working principle of Joule heating follows Joule’s law, which describes the energy conversion process that electric current generates heat when passing through conductive materials. When a pulsed or continuous voltage is applied to conductive catalyst precursors (such as carbon materials, metal salts doped conductive substrates and metal precursors), free electrons inside the material directionally move under the action of electric field and collide with atomic lattices, converting kinetic energy into internal thermal energy, thereby realizing synchronous and integral heating of the entire material . The heat generation can be quantified by the formula: Q=I²Rt, where Q represents the generated heat, I refers to the applied current, R stands for the resistance of precursor materials, and t is the electrification duration.
The entire Joule heating synthesis process can be divided into three core stages. Firstly, in the preheating stage, the applied low-intensity current preliminarily heats the conductive carrier to eliminate residual moisture and volatile impurities in the precursors. Secondly, the flash heating stage, the core of the whole process, applies high-intensity instantaneous current to raise the material temperature to 1500–3000 K within dozens of milliseconds, completing the rapid nucleation, growth and phase rearrangement of catalytic active components. Finally, the rapid quenching stage cuts off the power supply instantly, and the material cools down to room temperature rapidly at a rate of thousands of degrees per second. The rapid cooling process can lock the high-temperature metastable crystal phase and unique defect structure generated during the flash heating period, endowing the catalysts with extraordinary catalytic properties that cannot be obtained via traditional heating methods .
3. Unique Advantages for Catalyst Synthesis
3.1 Ultra-high Synthesis Efficiency and Low Energy Consumption
Traditional furnace-based synthesis requires long-time temperature rise, constant-temperature annealing and natural cooling, with a single synthesis cycle lasting 3–10 hours. In contrast, Joule heating can complete the whole catalyst preparation process within 10–60 seconds. The internal heating mode avoids redundant heating of external equipment and surrounding environment, which reduces invalid energy consumption by more than 80% compared with traditional calcination methods . Such high-efficiency and low-energy-consumption characteristics make Joule heating a revolutionary alternative to traditional thermal synthesis technologies.
3.2 Regulable Microstructure and Abundant Defective Active Sites
The ultra-fast heating and quenching characteristics of Joule heating can effectively suppress the overgrowth and agglomeration of active nanoparticles, realizing the controllable preparation of ultrafine nanocrystals and atomically dispersed single-atom active sites. Moreover, the transient high-temperature environment can induce rich lattice defects, oxygen vacancies and heteroatom doping defects inside catalysts. These defective structures can optimize the adsorption energy of reaction intermediates, adjust the electronic structure of active centers, and significantly enhance the intrinsic catalytic activity of materials . In addition, by adjusting electrical parameters such as current intensity, electrification time and pulse frequency, researchers can precisely control the crystallization degree and phase composition of catalysts to meet the performance requirements of different catalytic reactions.
3.3 Excellent Scalability and Versatility
Joule heating technology has strong compatibility with various types of precursor materials, including carbon-based materials, metal alloys, metal oxides and composite materials, and is applicable to the preparation of diverse catalysts for electrocatalysis, photocatalysis and thermal catalysis . Meanwhile, relevant research has verified that confined flash Joule heating can realize kilogram-scale batch synthesis of Fe-N-C carbon-based catalysts, breaking the bottleneck that most emerging rapid synthesis technologies are limited to laboratory micro-scale preparation . The simple device configuration and flexible parameter adjustment also reduce the threshold for large-scale industrial promotion.
4. Typical Applications in Catalyst Synthesis
4.1 Electrocatalytic Catalysts for Energy Conversion
Electrocatalysis is the most mature application field of Joule heating-synthesized catalysts, covering hydrogen evolution reaction (HER), oxygen evolution reaction (OER), oxygen reduction reaction (ORR), carbon dioxide reduction reaction (CO2RR) and nitrate reduction reaction (NO3RR) . For alkaline water electrolysis for hydrogen production, researchers have successfully fabricated low-crystallinity Ru-Mo oxide alloy catalysts via rapid Joule heating. The unique porous low-crystallinity structure optimizes the Ru-H bond strength through electronic modulation, and the optimized catalyst exhibits an ultralow overpotential under alkaline conditions, with excellent long-term cycling stability . In addition, Joule heating can directly grow ordered sub-5 nm Pt3Fe intermetallic nanocrystals on reduced graphene oxide within 60 seconds. The obtained catalysts show outstanding electrocatalytic performance for ethanol oxidation, solving the problem of easy agglomeration of precious metal nanoparticles in traditional synthesis .
For rechargeable zinc-air batteries, Joule heating has been adopted to prepare various doped cobalt-based metal oxide catalysts including rock salt oxide and perovskite oxide. Transition metal heteroatom doping further enriches OER/ORR active sites, and the Fe-CoO composite catalyst achieves competitive overpotential and cycling lifespan, providing a new pathway for rapid structural screening of bifunctional electrocatalysts .
4.2 Single-Atom and High-Entropy Catalysts
Single-atom catalysts (SACs) with 100% atomic utilization have become a research hotspot in catalysis, yet realizing uniform atomic dispersion and avoiding metal atom agglomeration remains a major challenge in traditional synthesis. Relying on instantaneous high temperature and ultra-short reaction time, Joule heating can fix isolated metal atoms on carbon-based carriers to form stable M-Nx active structures. The confined Joule heating strategy can effectively inhibit the migration and aggregation of metal precursors, and efficiently synthesize high-quality Fe-N-C single-atom catalysts with abundant FeN4 active sites .
Besides, Joule heating shows unique advantages in the preparation of high-entropy alloy catalysts with multiple metal components. The transient ultra-high temperature can simultaneously reduce multiple metal precursors with different reduction potentials, and the rapid quenching process stabilizes the high-entropy disordered alloy structure. This method effectively overcomes the technical pain points of uneven component distribution and complex preparation process of high-entropy catalysts fabricated by traditional methods .
4.3 Photocatalytic and Environmental Remediation Catalysts
In the field of photocatalysis, Joule heating can modify the band structure of metal oxide photocatalysts and construct heterojunction composite structures. The abundant lattice defects generated during the flash heating process can serve as electron capture sites, inhibit the recombination of photogenerated electrons and holes, and improve the photocatalytic efficiency of catalysts. Related studies have confirmed that Joule heating-modified TiO2 and ZnO-based composite catalysts exhibit excellent performance in organic pollutant degradation and photocatalytic hydrogen production . In terms of environmental governance, the derived carbon-based composite catalysts can also be applied to the efficient removal of heavy metal ions and harmful gases in water bodies, with broad application prospects in environmental remediation.
5. Challenges and Future Perspectives
5.1 Current Technical Challenges
Despite the remarkable progress achieved by Joule heating in catalyst synthesis, this technology still faces several unresolved challenges restricting its further development and industrialization. First of all, the internal heat transfer mechanism and material phase evolution law under transient ultra-high temperature are not fully clarified. It is difficult to monitor the real-time temperature change and microscopic structural evolution of precursors during the millisecond-level flash heating process, which increases the difficulty of precise directional synthesis of catalysts. Secondly, the uniformity of large-scale synthesis needs to be improved. In the kilogram-scale preparation process, the uneven distribution of current inside bulk precursors will lead to temperature difference, resulting in inconsistent structure and performance of partial catalysts. Thirdly, the applicable precursor system still has limitations, and the synthesis effect on non-conductive catalytic materials is poor, requiring additional conductive carriers to assist heating .
5.2 Future Development Directions
In the future, the research of Joule heating for catalyst synthesis will focus on three major directions. To begin with, combine in-situ characterization technologies such as in-situ transmission electron microscopy and real-time spectral detection to reveal the microscopic reaction mechanism of transient heating, and establish a complete theoretical system for parameter-performance correlation. Furthermore, optimize the device structure and electric field loading mode, develop multi-stage pulse Joule heating technology, expand the scope of applicable precursor materials, and realize the controllable synthesis of non-conductive catalysts. Finally, further upgrade large-scale batch preparation equipment, optimize production parameters, reduce preparation costs, and promote the industrial application of Joule heating in the mass production of commercial electrocatalysts and photocatalysts .
6. Conclusion
As a disruptive rapid thermal processing technology, Joule heating breaks through the inherent defects of traditional external heating synthesis methods. With the advantages of ultra-fast reaction speed, low energy consumption, adjustable microstructure and good scalability, it has realized the efficient preparation of various high-performance catalysts including electrocatalysts, single-atom catalysts, high-entropy alloys and photocatalysts. The ultra-fast heating and quenching unique to Joule heating can create abundant defective active sites and stable metastable phases, which effectively boosts the catalytic activity and stability of materials. Although problems such as unclear transient reaction mechanism and insufficient large-scale synthesis uniformity still exist, with the continuous optimization of equipment devices and in-depth exploration of reaction mechanisms, Joule heating is expected to become a universal core technology for industrial rapid synthesis of catalysts, and provide strong technical support for the large-scale application of green energy conversion and environmental protection related technologies.
