Operando Interfacial Ionics

Introduction

Electrochemistry provides direct control over the electron free energy and thus a path to electrically probe and drive chemical reactions. In strong contrast, no versatile technique exists that controls the free energy of a specific ion directly and in isolation. This has led to a poor understanding of interfacial ionics.

Importance of Water Dissociation

Take, for example, water dissociation, which is of key relevance for many energy technologies, such as:

1. Producing green H2 in alkaline conditions
2. Bipolar membranes (BPMs) that generate acid and base using (renewable) electricity in electrodialysis

BPMs are unique because they isolate water dissociation spatially at a junction between two electrically isolating, but ionically conducting polymers. However, macroscopic BPMs do not provide x-y-z resolution.

Limitations of Current Understanding

These geometric constraints limit our scientific understanding about the fundamental underpinnings of water dissociation (WD). It is still not clearly understood what causes the kinetic barriers of WD at heterogeneous interfaces, let alone the influence of the catalysts' surface structures or local electrostatics.

Project Goals

In Orion, I want to scale down the ion-selective contacts of the BPM and develop ionomer pipette microscopy. By forming and controlling a microscopic BPM junction, we will resolve and study WD activity as a function of:

• Crystal facets
• Metal oxide clusters
• Bias-dependent surface speciation

Broader Implications

In general, water dissociation serves as an ionic test reaction to study the impact and link between local electrostatics and local acid-base chemistry, which is fundamentally important for interfacial ionics in general.

More broadly, developing a table-top setup to control the free energy of specific ions with microscopic precision could have tremendous impact across various disciplines. Examples include:

1. Interfacial ion transport in solid-state electrochemical systems
2. (De)hydrogenation in organic chemistry and enzyme function
3. Proton gradients and action potentials in biochemistry