Surface Facet Engineering in Nanoporous Gold for Low-Loading Catalysts in Aluminum–Air Batteries

Abstract

The performance of metal−air batteries and fuel cells depends on the speed and efficiency of electrochemical oxygen reduction reactions at the cathode, which can be improved by engineering the atomic arrangement of cathode catalysts. It is, however, difficult to improve upon the performance of platinum nanoparticles in alkaline electrolytes with low-loading catalysts that can be manufactured at scale. Here, the authors synthesized nanoporous gold catalysts with increased (100) surface facets using electrochemical dealloying in sodium citrate surfactant electrolytes. These modified nanoporous gold catalysts achieved an 8% higher operating voltage and 30% greater power density in aluminum−air batteries over traditionally prepared nanoporous gold, and their performance was superior to commercial platinum nanoparticle electrodes at a 10 times lower mass loading. The authors used rotation disc electrode studies, backscattering of electrons, and underpotential deposition to show that the increased (100) facets improved the catalytic activity of citrate dealloyed nanoporous gold compared to conventional nanoporous gold. The citrate dealloyed samples also had the highest stability and least concentration of steps and kinks. The developed synthesis and characterization techniques will enable the design and synthesis of metal nanostructured catalysts with controlled facets for low-cost and mass production of metal−air battery cathodes.

Enhanced electrochemical performance of 3‐D microporous nickel/nickel oxide nanoflakes for application in supercapacitors

“…This is due to the fact that, at lower scan rates, the electrolyte ions have longer time to get to the bulk of NiO nanoflakes, while, at higher scan rates, ion movement is limited to the near surface. [ 37 ] The highest specific capacitance of 720, 557, and 435 mFcm −2 was achieved at 5 mVs −1 for NiO samples deposited at 30n, 45, and 60 min, respectively. The charge storage process of an electrode material can be calculated from CV by plotting the peak current as a function of scan rate.…”

“…Therefore, conformal deposition of metal oxide on 3‐D porous metal not only improves electrical conductivity but also provide binder‐free electrode materials. [ 35 ] In fact, nanoporous gold (Au) with interconnected porous network is widely used for energy storage and conversion devices, such as batteries, [ 36 ] supercapacitors, [ 37 ] and electrocatalysis. [ 38 ] However, the high cost of gold hindered its use for commercial and bulk of the applications.…”

Electroless Dealloying of Thin-Film Nanocrystalline Au–Ag Alloys: Mechanisms of Ligament Nucleation and Sources of Its Synthesis Variability

“…Aside from data mining studies, individual reports have focused on understanding process–structure relationships by fixing all process inputs to study the morphology of dealloyed NPG films as a function of dealloying conditions, such as with or without applying electrical bias, temperature, and time; − postannealing treatment; parent alloy composition and its effect on open-circuit potential; substrate preannealing; ternary alloys and impurities; etching solution concentration; , and stirring rate . Due to the lack of standardization across these studies, it becomes difficult to predict how these factors can be combined to alter process–structure relationships.…”

“…31 However, NPG solid area fraction could not be correlated to either structural characteristics (i.e., ligament diameter and length, parent alloy composition) or synthesis parameters (i.e., dealloying time and temperature), except for ligament aspect ratio 29 and, thus, independent control of ligament diameter and solid area fraction remains unexplained albeit clearly possible. Aside from data mining studies, individual reports have focused on understanding process−structure relationships by fixing all process inputs to study the morphology of dealloyed NPG films as a function of dealloying conditions, such as with or without applying electrical bias, 32 temperature, and time; 33−35 postannealing treatment; 36 parent alloy composition 37 and its effect on open-circuit potential; 38 substrate preannealing; 39 ternary alloys and impurities; 40 etching solution concentration; 41,42 and stirring rate. 43 Due to the lack of standardization across these studies, it becomes difficult to predict how these factors can be combined to alter process− structure relationships.…”

Robust Metallic Actuators Based on Nanoporous Gold Rapidly Dealloyed from Gold–Nickel Precursors

“…[ 1 ] Due to the high specific surface area, nanosized channels, monolithic body versus nanoparticles, excellent electrical conductivity, and mechanical strength versus nanoporous polymers or ceramics, nanoporous metals have wide applications from energy storage/conversion to CO 2 reduction. [ 2 ] Dealloyed nanoporous gold (np‐Au), in particular, has been utilized as a model material to study dealloying mechanisms, [ 1a,3 ] nano‐mechanics [ 4 ] and electro‐chemo‐mechanics, [ 5 ] or for applications in electrocatalysis, [ 6 ] supercapacitors, [ 7 ] batteries, [ 8 ] sensors, [ 9 ] and actuators. [ 10 ] These applications rely on the high surface‐area‐to‐volume ratio of np‐Au; in other words, a stable nanoporous structure that does not change or decay.…”