Insights into the deposition of nanostructured nickel oxides by amino acid chelated Complexes: Benefits of mixed side chains in the formation of nanostructures for Energy-efficient Electrochromic windows

[Display omitted] •Monitoring for deposition of nickel oxides from amino acid complexes via X-ray absorption fine structure spectroscopy in the hard and soft X-ray regions.•Slow deposition of nickel oxides results from the less conformational freedom and bulky nature of phenylalanine.•Ni(II) − L-alanine complex lead to the deposition of a homogeneous film with small grain size compared to Ni(II) − phenylalanine complex.•L-alanine and phenylalanine are present near the sample surface.•Bulky phenylalanine side chain passivates the sample surface, thereby lowering the transmittance loss. Electrochromic (EC) windows enhance the energy efficiency of climate control systems in the building sector. Here, we evaluate a strategy for electrodeposition of a high-performance EC nickel oxide by controlled release of Ni(II) ions from amino acid ligands. We compare the structural properties and EC characteristics of the samples deposited from Ni(II)-L-alanine or Ni(II)-phenylalanine complexes. During the deposition process, a film containing closely packed nanodeposits was formed by rapid release of Ni(II) ions from L-alanine ligands. This structure led to a high coloration efficiency of 76.4 cm2/C and nearly 100% retention of the initial optical modulation value even after 60 cycles of coloration. In contrast, the slow release of Ni(II) ions from phenylalanine ligands resulted in the formation of conglomerated island structures, which caused a low coloration efficiency and poor cycling stability. However, the bulky aromatic side chains on phenylalanine could passivate the sample surface, thereby lowering the transmittance loss to 1.38% under 24 h voltage-off. The aromatic side chains also contributed to the charge transfer between the solid–liquid interface of the sample. Furthermore, the sample deposited from the mixed L-alanine and phenylalanine complexes show greatly improved EC performance without compromising its superior optical memory and fast charge transfer characteristics.