Liquid Metal-Templated Tin-Doped Tellurium Films for Flexible Asymmetric Pseudocapacitors

Abstract

Liquid metals can be surface activated to generate a controlled galvanic potential by immersing them in aqueous solutions. This creates energized liquid−liquid interfaces that can promote interfacial chemical reactions. Here we utilize this interfacial phenomenon of liquid metals to deposit thin films of tin-doped tellurium onto rigid and flexible substrates. This is accomplished by exposing liquid metals to a precursor solution of Sn 2+ and HTeO 2 + ions. The ability to paint liquid metals onto substrates enables us to fabricate supercapacitor electrodes of liquid metal films with an intimately connected surface layer of tin-doped tellurium. The tin-doped tellurium exhibits a pseudocapacitive behavior in 1.0 M Na 2 SO 4 electrolyte and records a specific capacitance of 184.06 F•g −1 (5.74 mF•cm −2 ) at a scan rate of 10 mV•s −1 . Flexible supercapacitor electrodes are also fabricated by painting liquid metals onto polypropylene sheets and subsequently depositing tin-doped tellurium thin films. These flexible electrodes show outstanding mechanical stability even when experiencing a complete 180°bend as well as exhibit high power and energy densities of 160 W•cm −3 and 31 mWh•cm −3 , respectively. Overall, this study demonstrates the attractive features of liquid metals in creating energy storage devices and exemplifies their use as media for synthesizing electrochemically active materials.

Liquid Metal Interface for Two-Precursor Autogenous Deposition of Metal Telluride–Tellurium Networks

“…(1) Two HTeO 2 + reduction peaks were observed, and the smaller peak was attributed to a two-step reduction process associated with the formation of metastable H 2 Te. 19,20,44 The measurement of the CV curve of individual precursors was followed by the measurement under the same conditions but with the presence of both the metal ions (Ag + or Cu 2+ ) and the HTeO 2 + ions. The reduction onset and peak potentials of the , the reduction onset for Ag + decreased from 0.50 to 0.40 V, while that of the Cu increased from 0.00 to 0.14 V. The reduction of HTeO 2 + of the Ag + -HTeO 2 + and Cu 2+ -HTeO 2 + shifted from −0.15 V to more negative values of −0.22 and −0.26 V, respectively.…”

“…16 The liquid metal−electrolyte interface offers an atomically smooth yet electrochemically active template for growing or depositing a range of precursors into thin layers, 17,18 which presents great tunability for synthesizing materials in the nanoscale. 19,20 The liquid metal−electrolyte interface normally provides a highly reducing autogenous surface potential, which is able to reduce a wide range of oxidizing ionic precursors by selecting a suitable electrolyte. 19−22 While it is relatively straightforward to apply the liquid metal−electrolyte template to singleprecursor systems, extending it to systems with two or multiple precursors is challenging.…”

“…The liquid metal–electrolyte interface normally provides a highly reducing autogenous surface potential, which is able to reduce a wide range of oxidizing ionic precursors by selecting a suitable electrolyte. − While it is relatively straightforward to apply the liquid metal–electrolyte template to single-precursor systems, extending it to systems with two or multiple precursors is challenging. The difference in electrochemical properties (e.g., reducing potential) of various precursors at the same liquid metal–electrolyte interface can give rise to competing deposition conditions and peculiar complexities.…”

“…These properties make gallium-based alloys particularly suitable for a wide range of applications in flexible electronics and soft robotics alongside chemical and electrochemical processes. − In the context of electrochemistry, one of the most intriguing merits of liquid metals is the dynamic liquid–liquid interface that is established when they are in contact with an immiscible electrolyte . The liquid metal–electrolyte interface offers an atomically smooth yet electrochemically active template for growing or depositing a range of precursors into thin layers, , which presents great tunability for synthesizing materials in the nanoscale. , …”

“…For example, the bismuth telluride compound phase has been shown to produce by reducing bismuth and tellurium ions at the interface between a eutectic gallium–indium (EGaIn) liquid metal and a nitric acid electrolyte . However, the reduction of tin and tellurium ions at the same liquid metal–electrolyte interface has been shown to generate tellurium with a crystalline phase doped with tin . Considering such an example, the codeposition using multiprecursors at the liquid metal–electrolyte interface should be further explored as it could be a promising synthesis approach for engineering phases and structures, which, however, remains underexplored.…”