(664d) Controlling Electrochemical Reactivity By Tuning the Activity of Water

The development of efficient renewable energy conversion and storage devices is one of the most important challenges of the 21^st century. Thus, it is essential to mitigate climate change by reducing CO₂ emissions. This can be addressed by using renewable electricity to manufacture chemical fuels and synthetic precursors, or by generating electricity with carbon-neutral fuel cell devices. However, these electrocatalytic processes are hampered by low efficiencies and poor reaction selectivity. This problem is caused by a lack of guiding principles for choosing reaction conditions that will lead to the preferred electrochemical activities. For example, the role of water, a central solvent for most electrochemical reactions, is poorly understood.

Water is the principal proton donor for electrochemical reactions which take place at pHs > 7. Many reactions involve proton transfer steps; therefore, the supply of the proton donor (i.e. water) to the interface will have a substantial impact on reactivity and selectivity. A new type of aqueous system known as water-in-salt electrolyte (WISE) reduce the activity of water. In this talk I will discuss our efforts on elucidating the role of water in controlling the bifurcation of CO₂ electro-reduction between C₂₊ and C₁ products by utilizing NaClO₄-based WISE electrolytes. We demonstrated that the C₂₊/C₁ ratios were enhanced up to 20x by reducing the water activity (a_w) from 0.97 to 0.47, demonstrating unrivaled tunability between C₁ and C₂₊ products on the same electrode. Furthermore, kinetic analysis revealed that C₂ products exhibited negative reaction orders across a wide range of a_w; demonstrating that the restricted water supply enhanced their formation at the expense of C₁ products