3D printing technology has definitively come a long way since it was first invented in the early 1990s. Known as fuse deposition modeling, it was initially used to allow manufacturers to create, test, and examine an object more closely before producing a finished product.
Currently, 3D printing is widely adapted across sectors from commercial products to medical and electronic fabrication, due to the increasing demand for rapid and more efficient manufacturing of miniaturized complex objects using a variety of materials. Our research team has thus focused on the fabrication of 3D printed electrodes using a conventional 3D printer and explored its electrochemical properties in a different research field.
An electrode is a solid electric conductor that carries electric current into non-metallic solids, or liquids, or gases. Electrodes are typically electric conductors, but they need not be metals. For instance, typical materials used for electrodes in analytical chemistry are amorphous carbon, platinum, and also chemically-modified glass; in batteries, a variety of electrodes such as nickel, zinc, and other composite materials are used, depending on the battery type.
In order to continue the exploration of electrode materials, we modified the traditional plastic material into a conductive platform, which can conduct electricity and be utilized as an electrode material. The plastic materials that we used is called polylactic acid, or PLA. It is a biodegradable thermoplastic derived from renewable resources such as corn starch and sugarcane. The thermoplastic property of PLA makes it a suitable candidate in 3D printing techniques due to its low glass transition temperature (60-65oC) and high tensile strength (2.7 – 16 MPa). Nevertheless, modification of the polymeric structure of PLA is crucial in order to make it an electrical-conducting material for electrode applications.
Interestingly, through our previous research experience on nanomaterial synthesis, we have discovered a fascinating nanomaterial which can turn any plastic into a conductive material — and it is called graphene. Graphene is a one-atom-thick planar sheet of carbon atoms which are tightly arranged in an extended 2D honeycomb network. The first single layered graphene was mechanically exfoliated from its 3D allotrope, graphite through a “Scotch tape” method in 2004. Single layer graphene possesses abundant delocalized electron clouds on the surface, which facilitate the electron mobility and provide low surface resistivity.
These exceptional electrical advantages of graphene provide a significant improvement in the electronic properties of PLA. In addition, graphene is accredited for being one of the strongest materials ever discovered, due to its highly-ordered molecular structure and bonding arrangement between the hybridized carbon atoms. Polymer matrix composites with graphene fillers have shown tremendous improvements in elastic properties, tensile strength, thermal stability, and even electrical conductivity, due to the high surface area (2360 m2 g-1) and strong mechanical properties (~1100 GPa of Young’s modulus) of graphene.
In our latest research, we have fabricated a 3D printed electrode using a graphene/PLA filament. Compare to its PLA counterpart, graphene/PLA can conduct electricity which is favorable for fabrication into an electronic device. By using a commercial 3D printer, we are managed to print out the electrode in a short period of time, with high precision. The product can be customized according to our preferences and also suit the individual requirement of each experiment. This method can provide a rapid and cost-effective approach to produce a customized architecture.
Also, we have electrodeposited nanoparticles such as polypyrrole on the electrode surface, and a symmetrical solid-state supercapacitor was demonstrated using a polymer electrolyte. Such an initiative was never reported in the research field before. Furthermore, for the first time, the utilization of 3D printed electrode in photoelectrochemical (PEC) sensing platform was being demonstrated in our research study, using cadmium sulfide nanoparticles as an active semiconductor material to detect metal ion in wastewater treatment.
The characterization process of the 3D printed electrode is also a crucial part of our research. We have implemented several electrochemical analyses and characterization techniques, such as field emission scanning electron microscope and Raman Spectroscopy. Scanning electron microscopy uses an appropriate amount of focused electron beam over the surface of a sample to create the image of the 3D printed electrode and magnify it using the electromagnetic field. The electron beam interacts with the sample, producing various signals that can be used to obtain useful information about the surface morphology and composition.
Such characterization techniques provide the structural and morphological properties of the 3D printed electrode and also the deposited nanomaterials. Furthermore, an X-ray diffraction analysis and an X-ray photoelectron spectroscopy provide chemical state information between the nanoparticles and the electrode surface.
Overall, the performance of the as-fabricated supercapacitor and PEC sensor using 3D printed electrodes has shown promising results compared to previously-reported articles. The PEC performance of the as-fabricated electrode materials, which convert the solar energy to electrochemical energy, can improve the energy conversion efficiency and provide clean and sustainable energy supply to the environment.
Due to the high photo-conversion efficiency, the application of the as-synthesized nanomaterials can be applied in solar thermal and high-efficiency renewable electricity technologies such as heat pumps, electrocatalysis, and other options. More importantly, it is now cheaper than traditional options and involves much less investment risk. Moreover, the as-fabricated 3D printed supercapacitor can also be implemented in the industry to provide a better option in energy management. It can be introduced quickly to “absorb” excess energy in times of low demand and release it in times of shortage. This reduces the peak price of electricity by reducing the dependence on high-priced power generators.
These findings are described in the article entitled Three-Dimensional Printed Electrode and Its Novel Applications in Electronic Devices, recently published in the journal Scientific Reports. This work was conducted by Chuan Yi Foo, Hong Ngee Lim, Mohd Adzir Mahdi, and Mohd Haniff Wahid from the Universiti Putra Malaysia, and Nay Ming Huang from the University of Xiamen Malaysia.