Electrochemistry has a long history, but has never been more important than today, and is one of the most exciting branches of science. Electrochemistry is at the centre of energy storage and utilisation technologies, in batteries, fuel cells and solar cells. It is finding expanding applications in sensing and diagnostic platforms, and presenting new possibilities for the creation of nanomaterials, functionalised surfaces and in electrosynthesis. These technologies have emerged because of inquisitive science. A famous example is the development of the battery by Volta more than two centuries ago, not as a means of energy storage and utilisation, but to counter an argument with Galvani about the origin of "animal electricity". Yet, where would we be today without the battery?

Fundamental elementary electrochemical processes are extremely challenging to study and are limited by conventional experimental capability, which tends to focus on the macroscopic (applications) world or (at best, but rare) mesoscale. We intend to make and prove the smallest possible electrode: an individual single atom, produced by the electro-reduction of a single ion. We shall determine the conditions whereby this process occurs and study electrochemical processes at the resulting single atom electrode. This ambitious goal will be achieved by marrying recent developments in nanoscale electrochemistry and imaging science. We shall use nanoscale pipette probes in a scanning electrochemical cell microscopy (SECCM) format to deliver metal ions in a controllable way to a series of tiny regions on a boron doped diamond transmission electron microscopy (TEM) grid, which will serve as an electrode to reduce the impinging ions to atoms. This grid will then be analysed by aberration corrected-scanning transmission electron microscopy (ac-STEM). We shall further explore and prove a bottom-up approach for the production of nanoclusters atom-by-atom. We shall investigate electrocatalytic processes at these single atom and few-atom electrodes, to understand how electrochemical processes scale from the smallest possible size upwards.
The beauty of the proposed approach is that after electrodeposition in one spot by SECCM, the nanopipette is withdrawn, translated laterally by a small distance and landed in a fresh, new spot for the next electrodeposition, in a process that is repeated to create a scanned array, typically of several thousand individual spots on a reasonable timescale. Thus, it will be possible to execute several thousand experiments (trials) in an experimental run that will allow a wide parameter space to be explored and analysed by ac-STEM in one scan experiment. This unique high throughput combinatorial microscopy approach is crucial for obtaining statistics on an inherently stochastic process and to provide direct proof of the experimental outcome.

(i) Deposition of single atoms. We shall study electrodeposition under conditions where the average outcome is a single atom on a surface, bounded by the limits of the stochastic nature of single molecule diffusion.
(ii) Atom-by-atom assembly of metal nanostructures and clusters. Our studies will provide unprecedented insight into nucleation and growth processes generally, at the very earliest stages, not previously accessible to investigation.
(iii) Electrochemical measurements will reveal electrode kinetics at individual atom scale electrocatalytic entities, and also insights on mass transport and double layer effects at this scale.
(iv) If time permits, we shall investigate whether it is possible to make individual bimetallic nano-alloys (of just 2 or few atoms).

Our work takes experimental electrochemistry to a new domain: the atom lengthscale and nanoscale timescale.