Influence of Cu and oxide content in CuAl layered double hydroxides on C₂₊-selective CO₂ electroreduction

The electrocatalytic reduction of CO₂ to multicarbon (C₂₊) products on copper-based catalysts is dictated by the dynamic reconstruction of the active sites. While copper-aluminium (CuAl) layered double hydroxides (LDHs) have emerged as promising pre-catalysts, the role of the initial precursor phase, specifically the transition from highly crystalline LDH to oxide-rich hybrid phases, and its influence on catalytic activity in near-neutral electrolytes remain less understood. In this study, Cu_xAl pre-catalysts were systematically investigated across Cu : Al ratios from 5 : 1 to 1 : 2 in aqueous K₂SO₄, with the electrolyte concentration adjusted to probe its complex role in activity. Under optimised conditions, using an oxide-rich 5 : 1 pre-catalyst, the faradaic efficiency for C₂₊ reached approximately 55.3% at 250 mA cm^-2 in a near-neutral environment. The selectivity toward C₂₊ is dependent on the amount of Cu present and the oxide richness, with intermediate Cu amounts providing a balance between the availability of Cu active sites and the Al-mediated structural stabilisation. In contrast, Al-rich compositions offer less favourable product distributions. Increasing the K₂SO₄ concentration modulates the cell voltage and C₂₊ product formation. This suggests that combined interfacial electrolyte effects, including shifted local pH gradients and cation-mediated stabilisation, regulate C-C coupling pathways. Physicochemical characterisation, particularly in situ Raman spectroscopy, and electrochemical measurements indicate that the initial stoichiometry of the CuAl LDH and the presence of oxides/hydroxides influence the nature of the reconstructed Cu-based catalyst, yielding behaviour consistent with the partial stabilisation of Cu⁺ under operating conditions. These results demonstrate that the Cu content of CuAl pre-catalysts, together with the interfacial electrolyte environment, plays a key role in directing CO₂ selectivity. This systematic study offers guidance on rationally tuning the precursor phase, oxide richness, and reaction environment of Cu-based electrocatalysts for high-rate CO₂ reduction in non-alkaline media.