Print-Light-Synthesis for Single-Step Metal Nanoparticle Synthesis and Patterned Electrode Production

Abstract

The fabrication of thin-film electrodes, which contain metal nanoparticles and nanostructures for applications in electrochemical sensing as well as energy conversion and storage, is often based on multi-step procedures that include two main passages: (i) the synthesis and purification of nanomaterials and (ii) the fabrication of thin films by coating electrode supports with these nanomaterials. The patterning and miniaturization of thin film electrodes generally require masks or advanced patterning instrumentation. In recent years, various approaches have been presented to integrate the spatially resolved deposition of metal precursor solutions and the rapid conversion of the precursors into metal nanoparticles. To achieve the latter, high intensity light irradiation has, in particular, become suitable as it enables the photochemical, photocatalytical, and photothermal conversion of the precursors during or slightly after the precursor deposition. The conversion of the metal precursors directly on the target substrates can make the use of capping and stabilizing agents obsolete. This review focuses on hybrid platforms that comprise digital metal precursor ink printing and high intensity light irradiation for inducing metal precursor conversions into patterned metal and alloy nanoparticles. The combination of the two methods has recently been named Print-Light-Synthesis by a group of collaborators and is characterized by its sustainability in terms of low material consumption, low material waste, and reduced synthesis steps. It provides high control of precursor loading and light irradiation, both affecting and improving the fabrication of thin film electrodes.

Keywords: Print-Light-Synthesis; additive manufacturing; digital printing; electrochemistry; inkjet printing; nanomaterial synthesis; photochemical deposition; thin film electrodes.

Figure 1

General approaches to creating metal electrode patterns on a large scale based on precursor solutions. (A) Deposition of a metal precursor solution and subsequent thermal decomposition of the precursor. Thermal decomposition is an energy- and time-intensive process. (B) Deposition of a metal precursor ink with immediate photochemical reduction using high intensity light sources. High intensity flashlamps can reduce the photochemical process time to fractions of a second.

Figure 2

Exemplary routes for electrode patterning of metal nanoparticles that were synthesized by the interaction of electromagnetic radiation with metal precursor cations. (A) Schematic representation of photochemical metal nanoparticle synthesis with subsequent thin film fabrication. (B) Photocatalytic metal precursor reduction for the synthesis of photocatalytically active metal/semiconductor hybrid nanoparticles.

Figure 3

Schematic representation of Print-Light-Synthesis for electrode production. “Print” (left panel): Inkjet printing of a well-defined, confined ultra-thin reaction volume containing one or more dissolved metal precursor salts with highly controllable loading (e.g., few μg/cm²). Inkjet printing enables the fabrication of micrometrically resolved patterns. “Light” (central panel): Short irradiation of the as-deposited liquid precursor film converting the metal precursor into the desired material; the vicinity of the precursor to the substrate surface favors the deposition on the substrate rather than the synthesis of particles in the solution. “Synthesis”: The result of the process is a film of metal or mixed metal nanoparticles or nanostructures (depending on the process parameters), while all other ink components have been degraded and/or evaporated.

Figure 4

Print-Light-Synthesis of Pt nanoparticles and structures on indium tin oxide-coated glass slides. (A,B) Scanning electron micrographs demonstrate the presence of Pt nanostructures and/or nanoparticles on the substrate. (C) Cyclic voltammograms of a Pt/ITO electrode in nitrogen-saturated 0.1 M HClO₄ before (black) and after 7000 cycles performed in a separate measurement for oxygen reduction (red). Inset: Linear sweep voltammograms of a Pt/ITO electrode in oxygen-saturated 0.1 M HClO₄ before and after 7000 scans, scan rate 20 mV s⁻¹ (not IR-corrected). Figure adapted with permission from [3], Copyright 2018 John Wiley and Sons.

Figure 5

Print-Light-Synthesis with a high intensity Xe flashlamp for the creation of patterns of Pt on indium tin oxide-coated glass slides. Microscopic images demonstrating the effect of precursor loading optimization (A) and light energy density limit (B). Figure adapted with permission from [3], Copyright 2018 John Wiley and Sons.

Figure 6

Print-Light-Synthesis with a high intensity Hg arc lamp operated simultaneously to inkjet printing to fabricate thin gold film electrodes. The printing resolution can be increased by controlling the heat distribution in the light absorbing substrate. Placing the substrate on a metal plate transports the heat quickly away (A). Introduction of a layer of air, which is a poor heat conductor, increases the local temperature of the substrate limiting pattern widening (B). Figure reproduced with permission (open access article distributed under the terms of the Creative Commons CC BY license) from [26].

Figure 7

Print-Light-Synthesis of mixed Pt and Ir patterns (3.0 μg total metal precursors weight mm⁻²) on ITO -coated glass slides with different ratios of the two metal precursor inks. Column (A): mass ratio between platinum and iridium precursor; (B) (greyscale): scanning electron micrographs of the patterns of mixed Pt and Ir after Print-Light-Synthesis; (C) (green): EDX maps of Pt; (D): EDX maps of Ir; (D) (blue): EDX maps of Pt; (E): EDX peaks for Ir and Pt. Scale bar 400 μm. Details can be found in the experimental section.

Figure 8

Print-Light-Synthesis of mixed metal nanoparticles supported on carbon nanotubes. (a) Schematic representation of the PLS of a NiFe/CNT coated glassy carbon plate. The CNT layer acts as a light-to-heat converter to increase the precursor temperature for enhancing its reduction rate. Bright-field (b) and high-angle annular dark-field (c) STEM images of Ni_0.45Fe_0.55 NPs as formed on CNTs by Print-Light-Synthesis. (d) Electrochemical characterization of Ni/CNT/GC (solid line), Ni_0.45Fe_0.55/CNT/GC (dashed line and inset), and Fe/CNT/GC (dotted line). Electrolyte 0.1 M KOH, scan rate 50 mV s⁻¹, 20th cycle with vertex potentials 0.25 and 1.75 V (an excerpt from the CV between 1.00 V and 1.60 V is plotted). Not IR-corrected. Adapted with permission from [50]. Copyright 2019 American Chemical Society.

Figure 9

Oxidative Print-Light-Synthesis of patterns of Prussian Blue electrodes. (A) Optical photographs directly after inkjet printing of the PB precursor ink and after inkjet printing and flashlight exposure of the as-obtained PB patterns. (B) Electrochemical characterization at 10 mV s⁻¹ in argon-saturated 1 M KCl + 5 mM HCl (pH = 2.34) of the PB electrode obtained using Print-Light-Synthesis (solid red line) and using conventional PB synthesis (dashed blue line). Adapted with permission from [53]. Copyright 2020 American Chemical Society.