Enzymes are characterized by an active site that is typically embedded deeply within the protein shell thus creating a nanoconfined reaction volume in which high turnover rates occur. We propose nanoparticles with etched substrate channels as a simplified enzyme mimic, denominated nanozymes, for electrocatalysis. We demonstrate increased electrocatalytic activity for the oxygen reduction reaction using PtNi nanoparticles with isolated substrate channels. The PtNi nanoparticles comprise an oleylamine capping layer that blocks the external surface of the nanoparticles participating in the catalytic reaction. Oxygen reduction mainly occurs within the etched channels providing a nanoconfined reaction volume different from the bulk electrolyte conditions. The oxygen reduction reaction activity normalized by the electrochemically active surface area is enhanced by a factor of 3.3 for the nanozymes compared to the unetched nanoparticles and a factor of 2.1 compared to mesoporous PtNi nanoparticles that possess interconnecting pores.

The use of nanoparticles and nanostructured electrodes are abundant in electrocatalysis. These nanometric systems contain elements of nanoconfinement in different degrees, depending on the geometry, which can have a much greater effect on the activity and selectivity than often considered. In this Review, we firstly identify the systems containing different degrees of nanoconfinement and how they can affect the activity and selectivity of electrocatalytic reactions. Then we follow with a fundamental understanding of how electrochemistry and electrocatalysis are affected by nanoconfinement, which is beginning to be uncovered, thanks to the development of new, atomically precise manufacturing and fabrication techniques as well as advances in theoretical modeling. The aim of this Review is to help us look beyond using nanostructuring as just a way to increase surface area, but also as a way to break the scaling relations imposed on electrocatalysis by thermodynamics.

Nanoparticles mimicking the three-dimensional architecture of enzymes where the reaction occurs down a channel isolated from bulk solution, referred here as nanozymes, were used to explore the impact of nano-confinement on electrocatalytic reactions.

Nanozymes mimic enzymes and that includes their selectivity. To achieve selectivity, significant inspiration for nanoparticle design can come from the geometric and molecular features that make enzymes selective catalysts. The two central features enzymes use are control over the arrangement of atoms in the active site and the placing of the active site down a nanoconfined substrate channel. The implementation of enzyme‐inspired features has already been shown to both improve activity and selectivity of nanoparticles for a variety of catalytic and sensing applications. The tuning and control of active sites on metal nanoparticle surfaces ranges from simply changing the composition of the surface metal to sophisticated approaches such as the immobilization of single atoms on a metal substrate. Molecular frameworks provide a powerful platform for the implementation of isolated and discrete active sites while unique diffusional environments further improve selectivity. The implementation of nanoconfined substrate channels around these highly controlled active sites offers further ability to control selectivity through altering the solution environment and transport of reactants and products. Implementing these strategies together offers a unique opportunity to improve nanozyme selectivity in both sensing and catalysis.

Die Verwendung von Nanopartikeln und nanostrukturierten Elektroden ist in der Elektrokatalyse weit verbreitet. Diese nanometrischen Systeme enthalten je nach Geometrie Elemente des Nanoconfinements in unterschiedlichem Ausmaß, was sich viel stärker auf die Aktivität und Selektivität auswirken kann, als oft angenommen wird. In diesem Aufsatz identifizieren wir zunächst die Systeme, die unterschiedliche Grade von Nanoconfinement enthalten, und zeigen, wie sie die Aktivität und Selektivität elektrokatalytischer Reaktionen beeinflussen können. Anschließend wird ein grundlegendes Verständnis der Auswirkungen des Nanoconfinements auf die Elektrochemie und Elektrokatalyse vermittelt, das dank der Entwicklung neuer, atomar präziser Herstellungs-und Fertigungstechniken und Fortschritten bei der theoretischen Modellierung allmählich erschlossen wird. Diese Übersicht soll dabei helfen, die Nanostrukturierung nicht nur zur Vergrößerung der Oberfläche zu nutzen, sondern auch die thermodynamisch bedingten Skalierungsbeziehungen in der Elektrokatalyse zu durchbrechen.