Preparing two-dimensional nano-catalytic combustion patterns using direct inkjet printing

Highlights

• We demonstrate direct fabricating of two-dimensional catalytic combustion patterns.

• IJP method realized ultra low loading and high utilizing of Pt catalysts.

• Spontaneous combustion is achieved at room temperature and small scale (∼800 μm).

• Accurate temperature control makes the catalyst an adjustable power source.

Abstract

Two-dimensional catalytic combustion patterns, which can be used as heat source in micro-nano scale MEMS devices such as gas sensor and micro-generator, are fabricated by inkjet printing (IJP). The performances of the catalytic patterns are evaluated by both traditional catalytic activity measurement and infrared thermography (IR) camera. Results show that ultra-low (0.014 mg cm⁻²) loading and high utilizing (34,710 mW mg⁻¹) of Pt catalysts can be achieved by inkjet printing method. Spontaneous combustion is also observed for the printed Pt/Al₂O₃ powder membrane at rather low initiation temperature and small scale. The IR camera analysis indicates the uniform temperature distribution and rapid temperature response of the micro-patterned catalyst surface. With the advantages of the inkjet printing, this new direct-write method would, in principle, open up possibilities of these special catalyst patterns serving as micro energy sources for MEMS applications.

Introduction

Micro heater fabricated by MEMS technology, possessing advantages of small size, fast thermal response, high temperature at low power consumption, has gained specific attention as they are key constituent parts in micro-sensors such as wind sensors [1], humidity sensors [2] and gas sensor [3]. Another kind of heat source at small scale is catalytic combustor, normally used in micro-machined thermoelectric hydrogen sensors (micro-THS) [4], [5], [6]. Unlike the MEMS-based micro heater converting electric energy into stable heat energy, the catalytic combustor turn chemical energy into heat at low combustion temperature with extraordinary high energy density [7]. Furthermore, lower combustion temperature of catalytic combustion makes thermal stresses and heat losses less problematic [8]. Still, catalytic combustion acting as power supply for MEMS devices remains difficult, owing to the obstacles of reducing catalyst size below 1 mm², shape controlling, uniform temperature distribution on catalyst surface and self-ignition of catalyst at room temperature.

Traditional ways like screen printing have been investigated for catalyst deposition. Although screen printing is a simple, cost-effective coating technique, this method do have disadvantages like uniformity, direct-contact of printing surface which may bring damage to the fragile device structure when applying in MEMS. Furthermore, screen printing is not qualified for ultra low (<0.5 mg cm⁻²) condition. Inkjet printing (IJP) is a technology for micro scale patterning, jetting solutions or turbid liquid with small particle size onto addressable sites on a specific substrate, flexible or inelastic. It has been considered as an alternative of lift-off process, since inkjet printing can achieve direct patterning without any masks at small scale [9]. It also has promising prospects in fields such as organic field-effect transistors (OFETs) [10], conductive features [11], [12], sensor [13], polymer light-emitting diode (PLED) [14], [15], radio frequency identification (RFID) tags [16], and fuel cell [17], [18], etc. In general, it's more controllable, material saving and compatible with MEMS devices.

In this paper, we develop a rapid prototyping technique to fabricate Pt nano-catalytic patterns for use as a micro heater in MEMS devices. Chloroplatinic acid solution was chosen as the catalyst precursor ink to produce catalyst patterns at predefined position with different shapes. Catalysts characteristics including catalytic activity, catalytic combustion performance, temperature distribution and temperature response rate were investigated.