Conjugated polymers such as polyethylenedioxythiophene (pEDOT), polypyrrole (pPy), and polyaniline (pAni) exhibit high electrochemical capacities, making them appealing as electrode materials for energy storage, electrochemical desalination, and chemical sensing. Recent work has established the growth of thin films of pEDOT using alternating gas-phase exposures of the EDOT monomer and a metal chloride (e.g., MoCl 5 ) oxidant in a process termed oxidative molecular layer deposition (oMLD). Here, we describe the first demonstration of oMLD of amine-containing conjugated polymers. We find that pyrrole (Py) and MoCl 5 undergo self-limiting surface reactions during oMLD exposures to form conformal pPy thin films, but oMLD using aniline (Ani) and p-phenylenediamine (PDA) monomers yields unexpected azo functionality. The formation of azo groups is attributed to an MoCl 5 -amine surface adduct that spatially constrains polymerization reactions near the amine group and produces azo groups when coupling two primary amines. pPy grown by oMLD exhibits a record-breaking 282 mAh/g capacity in an aqueous electrolyte, and PDA/MoCl 5 oMLD yields azo polymers of interest as anode materials for alkali-ion batteries. Alternating between Py and PDA monomers during oMLD produces molecularly assembled copolymers with qualitatively different electrochemical responses from the isolated monomer structures. This work lays the foundation for the growth of conformal thin films of conjugated amine polymers with molecular-level control of composition and thickness.

Electrode materials which undergo anion insertion are of interest for next-generation energy storage devices and electrochemical water desalination. Polyaniline (PANI) is a robust and well-studied electrode material for anion insertion, but to date we have been unable to establish the electrochemical and anion-binding performance of PANI at nanoscale thicknesses because these thicknesses are not obtainable using standard PANI deposition procedures. Here, we report a new pulsed electrodeposition procedure for the controlled growth of PANI thin films with nanometer-scale thickness control. Using this pulsing technique, we deposit nanoscale (<100 nm) thin films of PANI onto stainless steel (SS) disks and gold electrochemical quartz crystal microbalance (EQCM) crystals. We examine the charge rate and anion-binding properties as a function of nanoscale thickness, and reveal previously undescribed insights into the charge storage and anion binding mechanisms of PANI. In particular, we identify that PANI films of <10 nm thickness provide rapid chloride ion uptake for desalination applications, and that thicker ∼100 nm PANI films are able to achieve rapid charge storage in sulfate solutions due to SO 4 2− /HSO 4 − embedded within the PANI acting as a proton donor/ acceptor. The results we report will inform the use of PANI thin films for energy storage and desalination applications.

Oxidative molecular layer deposition (oMLD) promises to enable molecular-level control of polymer structure through monomer-by-monomer growth via sequential, self-limiting, gas-phase surface reactions of monomer(s) and oxidant(s). However, only a few oMLD growth chemistries have been demonstrated to date, and limited mechanistic understanding is impairing progress in this field. Here, we examine oMLD growth using 3,4-ethylenedioxythiophene (EDOT), pyrrole (Py), p-phenylenediamine (PDA), thiophene (Thi), and furan (Fu) monomers. We establish key insights into the surface reaction mechanisms underlying oMLD growth. We specifically identify the importance of a two-electron chemical oxidant with sufficient oxidation strength to oxidize both a surface and a gas-phase monomer to enable oMLD growth. The mechanistic insights we report enable rational molecular assembly of copolymer structures to improve electrochemical capacity. This work is foundational to unlock molecular-level control of redox-active polymer structure and will enable the study of previously intractable questions regarding the molecular origins of polymer properties, allowing us to control and optimize polymer properties for energy storage, water desalination, and sensors.

Poly(3,4-ethylene dioxythiophene) (PEDOT) has a high theoretical charge storage capacity, making it of interest for electrochemical applications including energy storage and water desalination. Nanoscale thin films of PEDOT are particularly...

Area-selective atomic layer deposition (AS-ALD) techniques are an emerging class of bottom-up nanofabrication techniques that selectively deposit patterned ALD films without the need for conventional top-down lithography. To achieve this patterning, most reported AS-ALD techniques use a chemical inhibitor layer to proactively block ALD surface reactions in selected areas. Herein, an AS-ALD process is demonstrated that uses a focused electron beam (e-beam) to dissociate ambient water vapor and "write" highly resolved hydroxylated patterns on the surface of highly oriented pyrolytic graphite (HOPG). The patterned hydroxylated regions then support subsequent ALD deposition. The ebeam functionalization technique facilitates precise pattern placement through control of beam position, dwell time, and current. Spatial resolution of the technique exceeded 42 nm, with a surface selectivity of between 69.9% and 99.7%, depending on selection of background nucleation regions. This work provides a fabrication route for AS-ALD on graphitic substrates suitable for fabrication of graphene-based nanoelectronics.