3D Printed Nickel–Molybdenum-Based Electrocatalysts for Hydrogen Evolution at Low Overpotentials in a Flow-Through Configuration

Abstract

Three-dimensional (3D) printed, hierarchically porous nickel molybdenum (NiMo) electrocatalysts were synthesized and evaluated in a flow-through configuration for the hydrogen evolution reaction (HER) in 1.0 M KOH­(aq) in a simple electrochemical H-cell. 3D NiMo electrodes possess hierarchically porous structures because of the resol-based aerogel precursor, which generates superporous carbon aerogel as a catalyst support. Relative to a traditional planar electrode configuration, the flow-through configuration allowed efficient removal of the hydrogen bubbles from the catalyst surface, especially at high operating current densities, and significantly decreased the overpotentials required for HER. An analytical model that accounted for the electrokinetics of HER as well as the mass transport with or without the flow-through configuration was developed to quantitatively evaluate voltage losses associated with kinetic overpotentials and ohmic resistance due to bubble formation in the porous electrodes. The chemical composition, electrochemical surface area (ECSA), and roughness factor (RF) were also systematically studied to assess the electrocatalytic performance of the 3D printed, hierarchically porous NiMo electrodes. An ECSA of 25163 cm2 was obtained with the highly porous structures, and an average overpotential of 45 mV at 10 mA cm–2 was achieved over 24 h by using the flow-through configuration. The flow-through configuration evaluated in the simple H-cell achieved high electrochemical accessible surface areas for electrochemical reactions and provided useful information for adaption of the porous electrodes in flow cells.

3D-printing design for continuous flow catalysis

“…Remarkably, the use of a resol-based aerogel precursor resulted in the formation of a superporous carbon support, reaching an electrochemical surface area of 25 163 cm 2 . In the aforementioned contribution, Xiang and coworkers also accomplished a study regarding the electrokinetics and the mass transport of the reaction under both flow-through and planar configurations [69].…”

Low Tortuosity 3D‐Printed Structures Enhance Reaction Kinetics in Electrochemical Energy Storage and Electrocatalysis

“…[91] Recently, 3D-printed lattice structures with open large low-tortuous channels have been developed for tackling bubble migration. [31,92,93] Kou et al showed that a 3D-printed Ni lattice electrode with high surface area and low-tortuous channels can mitigate gas bubble traffic during alkaline water electrolysis at high current densities (Figure 17a). [31] The periodic porous electrode allows rapid bubble movement and releasing, achieving low HER (245 mV) and OER (425 mV) overpotentials at the ultrahigh current density of 1000 mA cm À2 , respectively.…”

“…OER 425 mV @ 1000 mA cm À2 NiMo HER 1.0 M KOH aq. 45 mV @ 10 mA cm À2 24 h @ 10 mA cm À2 [92] Stainless steel OER 1.0 M KOH with 0.6 M NaCl aq.…”

Rational 3D Structure of Monolithic Catalysts for Enhanced Hydrolytic Dehydrogenation of Ammonia Borane

“…Rational three-dimensional (3D) structure at a macrolevel can optimize the bubble transport path and suppress the severe bubble coalescence in the local structure to enable the full exploitation of the intrinsic activity of the catalyst. − It is supposed to be a promising path to further promote the mass transfer under industrial-scale high hydrogen evolution rate but is often overlooked due to the constrained choice of 3D substrates, such as Ni foam and Ti mesh. − However, even for the state-of-the-art 3D structures, the specific surface area exhibits a “seesaw” relationship with the bubble transport capacity since the larger specific surface area tends to have more complex structures with small pore sizes. , For example, for commercial nickel foam (NF), the most common 3D substrate, although its porous structure leads to increased active sites, its mass transport ability is seriously limited by the bubble trapping caused by the randomly oriented pores throughout the structure . This means that the structural design of 3D catalysts under different conditions requires a focus between the chemical reaction zone and mass transfer; therefore, rational 3D structures of monolithic catalysts are urgently needed to balance the structural influence factors for maximizing performance, but the related studies have never been reported.…”