Abstract: Carbon-based 3D hierarchical electrodes with appropriate spatial distributions of pores are expected to empower rapid and controllable electrochemical reactions. The ability to fabricate such an electrode, with tunable geometries comprised of continuous nano- and micro-conduits, allows simultaneous optimization of conversion capacity as well as reaction rate. Such manufacturability holds great potential to redefine the future of energy storage, electrocatalysis and chemical production for a sustainable future. In this presentation, I will outline two convergent strategies that involve the integration of additive manufacturing with several decades of advancements in nanomaterials synthesis, coupled with conventional pyrolysis – for creating such electrodes. The primary structure of 3D carbon-based electrodes was fabricated by either direct 3D writing, or the transition metal assisted pyrolysis of 3D-printed polymer templates. The secondary structure was established by employing bottom-up synthesis approaches: (a) SiO2 nanoparticle templates to create nanoscopic porous structures or (b) nanochannels formed through direct growth of carbon nanotubes. We have demonstrated that the primary and secondary structures can be formed by a single step. After monolithic integration of a tertiary structure to reveal sites for electrochemical conversion, these 3D architected electrodes offer impressive charge storage capacities while maintain excellent rate capability. By exploiting the short mass diffusion lengths, we have demonstrated that the new energy storage devices can operate at temperatures as low as -70°C without the requirement of a heater. Furthermore, the incorporation of a high loading of active materials in our 3D electrodes allows for concurrent enhancement of both energy density and power density. These scalable fabrication protocols address two critical challenges – sluggish mass transfer in 3D and the lack of accessible active sites, thereby offering a pathway to harness electrochemical reactions in 3D. This work offers an adaptable solution across a broad spectrum of industries.

In an era marked by a growing demand for sustainable and high-performance materials, the convergence of additive manufacturing (AM), also known as 3D printing, and the thermal treatment, or pyrolysis, of polymers to form high surface area hierarchically structured carbon materials stands poised to catalyze transformative advancements across a spectrum of electrification and energy storage applications. Designing 3D printed polymers using low-cost resins specifically for conversion to high performance carbon structures via post-printing thermal treatments overcomes the challenges of 3D printing pure carbon directly due to the inability of pure carbon to be polymerized, melted, or sintered under ambient conditions. In this perspective, we outline the current state of AM methods that have been used in combination with pyrolysis to generate 3D carbon structures and highlight promising systems to explore further. As part of this endeavor, we discuss the effects of 3D printed polymer chemistry composition, additives, and pyrolysis conditions on resulting 3D pyrolytic carbon properties. Furthermore, we demonstrate the viability of combining continuous liquid interface production (CLIP) vat photopolymerization with pyrolysis as a promising avenue for producing 3D pyrolytic carbon lattice structures with 15 μm feature resolution, paving way for 3D carbon-based sustainable energy applications.

Electrochemical conversion of carbon dioxide (CO2) gas to value-added chemicals such as multicarbon (C2+) alcohols is a promising and attractive decarbonization strategy. However, there are tremendous challenges in tuning the intrinsic activity and selectivity of the catalysts to produce C2+ alcohols. In this work, we prepared a CeO2-Cu composite catalyst via a combination of metallurgy and dealloying method. The interfacial sites of amorphous CeO2-Cu heterostructure improve the adsorption of key reaction intermediates *CO and promote the C-C coupling. Significantly, they also stabilize *CH2CHO at the bifurcation step, steering the reaction pathway toward the formation of C2+ alcohols over ethylene. The CeO2-Cu catalyst achieves a remarkable faradaic efficiency of 32.9% +/- 2.6% for C2+ alcohols at -0.6 V vs RHE. This work demonstrates an effective strategy of improving the intrinsic activity and selectivity of the Cu-based catalysts for the generation of C2+ alcohols.

Aqueous rechargeable zinc-iodine batteries (ZIBs) are promising candidates for grid energy storage because they are safe and low-cost and have high energy density. However, the shuttling of highly soluble triiodide ions severely limits the device's Coulombic efficiency. Herein, we demonstrate for the first time a double-layered cathode configuration with a conductive layer (CL) coupled with an adsorptive layer (AL) for ZIBs. This unique cathode structure enables the formation and reduction of adsorbed I3- ions at the CL/AL interface, successfully suppressing triiodide ion shuttling. A prototypical ZIB using a carbon cloth as the CL and a polypyrrole layer as the AL simultaneously achieves outstanding Coulombic efficiency (up to 95.6%) and voltage efficiency (up to 91.3%) in the aqueous ZnI2 electrolyte even at high-rate intermittent charging/discharging, without the need of ion selective membranes. These findings provide new insights to the design and fabrication of ZIBs and other batteries based on conversion reactions.

A holistic approach to fabricate a hierarchical electrode that consists of redox-active poly(1,5-diaminonaphthalene), 1,5 PDAN, uniformly and conformally grafted onto a 3D carbon nanotube (CNT-a-CC) electrode is set forth. The CNT-a-CC electrode was formed by direct growth of high-density CNTs on the surface of every individual microfiber, the constituent of activated carbon cloth (a-CC). Owing to the naphthalene backbone, conformal deposition of 1,5 PDAN on carbon surfaces has been readily attained via electropolymerization. This hierarchical platform with open and continuous nanochannels formed by CNTs coupled with excellent electrical connectivity between CNTs and the polymer provides a reproducible platform for electrochemical investigation. According to multiple sample analyses on CNT-a-CC, the gravimetric capacitance of 1,5 PDAN is up to 1250 F/g, and this value can be maintained up to 100 mV/s. Hierarchical organization provides a specific capacitance of 650 F/g at 2 mV/s at a 1,5 PDAN loading of 2.5 mg/cm2. The conjugated ladder structure of the polymer led to strong π-π interactions between the polymer and CNT-a-CC together with mechanically robust CNT-a-CC. A capacitance retention of 94% for 1,5 PDAN has been obtained after 25,000 cycles at 100 mV/s, a significant cycle stability improvement over conventional conductive polymers such as polyaniline. This new lightweight electrode that seamlessly integrates functional species with nanochannel-like CNT-a-CC opens up a new opportunity to harness electrochemical reactions in the 3D carbon electrode for energy storage and electrocatalysis as well as electrochemical sensing.

In article number 2002955 Rui Wu, Cheng Zhu, Yat Li and co-workers demonstrate a new approach for the deterministic design of 3D electrodes to minimize the deleterious effects of gas bubbles by carefully engineering porous highways and transport networks that facilitate rapid bubble transport and release to enhance the total electrode catalytic activity at commercially relevant current densities.

Alkaline water electrolysis at high current densities is plagued by gas bubble generation and trapping in stochastic porous electrodes (e.g., Ni foams), which causes a significant reduction in the number of electrolyte accessible catalyst active sites. Here, 3D printed Ni (3DPNi) electrodes with highly controlled, periodic structures are reported that suppress gas bubble coalescence, jamming, and trapping and, hence, result in rapid bubble release. The 3DPNi electrodes decorated with carbon-doped NiO achieve a high current density of 1000 mA cm(-2)in 1.0mKOH electrolyte at hydrogen evolution reaction and oxygen evolution reaction overpotentials of 245 and 425 mV, respectively. This work demonstrates a new approach to the deterministic design of 3D electrodes to facilitate rapid bubble transport and release to enhance the total electrode catalytic activity at commercially relevant current densities.