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

Abstract 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.