Electrodeposited dendritic copper foams have been extensively studied as an electrocatalyst for CO2 reduction reaction (CO2RR). Many parameters, such as dendrite size, porosity, pore size, and crystal faceting, define the hierarchical properties of these structures and their subsequent bubble evolution and CO2RR capabilities. Herein, the effects the electrodeposition conditions (potential, pH) have on the resulting crystallinity, microstructure, and macroporosity of the copper foam are studied. These morphological differences and the corresponding effects on electrocatalytic activity are characterized. It is shown that the composition of the electrodeposition bath can have significant effects on the mechanics of bubble formation and detachment at the surface during hydrogen evolution reaction in acidic solutions. Similarly, the electrodeposition conditions for the synthesis of the foam affect the product selectivity during CO2RR electrocatalysis. Foams deposited in alkaline electrodeposition solutions show high faradaic efficiency and specificity toward C2H6, an uncommon product of CO2RR, at modest applied potentials (−0.8 V versus reversible hydrogen electrode.

Electrodeposited dendritic copper foams have been extensively studied as an electrocatalyst for CO2 reduction reaction (CO2RR). Many parameters, such as dendrite size, porosity, pore size, and crystal faceting, define the hierarchical properties of these structures and their subsequent bubble evolution and CO2RR capabilities. Here we studied the effects the electrodeposition conditions (potential, pH) have on the resulting crystallinity, microstructure, and macroporosity of the copper foam. We characterized these morphological differences and the corresponding effects on electrocatalytic activity. We showed that the composition of the electrodeposition bath can have significant effects on the mechanics of bubble formation and detachment at the surface during hydrogen evolution reaction (HER) in acidic solutions. Similarly, the electrodeposition conditions for the synthesis of the foam affected the product selectivity during CO2RR electrocatalysis. Foams deposited in alkaline electrodeposition solutions showed high faradaic efficiency and specificity towards C2H6, an uncommon product of CO2RR, at modest applied potentials (-0.8 V vs. RHE).

Ultra-thin film coatings are used to protect semiconductor photoelectrodes from the harsh chemical environments common to photoelectrochemical energy conversion. These layers add contact transfer resistance to the interface that can result in a reduction of photoelectrochemical energy conversion efficiency of the photoelectrode. Here, we describe the concept of a partial protection layer, which allows for direct chemical access to a small fraction of the semiconductor underlayer for further functionalization by an electrocatalyst. The rest of the interface remains protected by a stable, inert protection layer. CuO is used as a model system for this scheme. Atomic layer deposition (ALD)-prepared TiO2 layers on CuO thin films prepared from electrodeposited Cu2O allow for the control of interfacial morphology to intentionally expose the CuO underlayer. The ALD-TiO2 overlayer shrinks during crystallization, while Cu2O in the underlayer expands during oxidation. As a result, the TiO2 protection layer cracks to expose the oxidized underlying CuO layer, which can be controlled by preceding thermal oxidation. This work demonstrates a potentially promising strategy for the parallel optimization of photoelectrochemical interfaces for chemical stability and high performance.