The CO2 transformation via electrochemical reduction has been a longstanding target, considering the application of intermittent renewable energy sources. In such a system, the ability to produce liquid fuels is highly desirable due to their high energy density and security in storage and transportation, to which the design of electrocatalytic materials is the main focus. In this direction, Copper materials showed great promise to promote the selective electroreduction of CO2 to C2+ products with a high conversion efficiency. Research efforts have been made to improve the activity and selectivity of Cu-based electrocatalysts through doping or alloying with other transition metals. Nevertheless, the selectivity analysis requires a lot of time and several tests in order to find the proper configuration. This trial-and-error procedure is one of the main bottlenecks in the realization of performative electrodes.

Moreover, these electrocatalysts can be coupled to semiconductors to obtain photocathodes. Nowadays, metal–oxide-based ones are very popular. Nevertheless, Cu-based oxides are a known exception, and their rapid photo-corrosion under cathodic bias in aqueous media poses as their most prohibitive limitation.

In this study, we investigate Cu–Ti [1] and Cu–Sn [3] heterostructured catalysts to elucidate how compositional variations influence electrocatalytic performance and product selectivity during the CO2 reduction reaction (CO2RR). Using magnetron co-sputtering in a high-throughput configuration, we fabricated compositional gradients of Ti and Sn on super-polished Si substrates and FTO supports. Local electrochemical characterization was performed with a scanning flow (photo)electrochemical cell, enabling rapid screening of catalyst libraries and identification of optimal compositions. This approach revealed that 5 at.% Ti in Cu–Ti and 10 at.% Sn in Cu–Sn yields the most promising electrochemical responses. Following compositional optimization, selectivity analyses were conducted using HPLC and micro-GC to quantify liquid and gaseous CO2RR products, respectively. Overall, the combined high-throughput synthesis and localized characterization strategy significantly accelerated catalyst evaluation and facilitated the identification of highly selective Cu-based heterostructures for CO2 reduction.

In addition to that, those catalysts were coupled with a semiconductor, in particular, electrodeposited Cu2O electrodes with TiO2 as a passivation layer, to study their stability and performance under both light and dark configurations.