Electrochromic Adaptability of NiO_x Films Modified by Substrate Temperature in Aqueous and Non‐Aqueous Electrolytes

Abstract

Depending on adjusting substrate temperature during film depositing, a series of NiOx films has been prepared by magnetron sputtering. The electrochromic (EC) advantage of NiOx films modified by substrate temperature is verified. Moderate heating substrate can improve surface charge transfer (from ≈30 to ≈40 mC cm−2) and energy storage capacity (45% increment) without damaging other performance effectively. Considering the different electrochemical mechanisms in varied electrolytes, the EC performance of NiOx films in two electrolytes is discussed. In KOH electrolyte, NiOx films at 300 °C substrates show prominent optical modulation (≈81%) and high charge capacity (≈40 mC cm−2). 300 °C heating compensates for the shortage of poor stability and tedious activation. In LiClO4‐PC electrolyte, NiOx films can undergo long‐term cycles compared with aqueous conditions, the coloration efficiency keeps high level (≈80 cm2 C−2) which means small charge quantities can drive a wide transmittance range. The cyclic discrepancy in two electrolytes can be ascribed to diverse reacted modes between electrolyte ions and NiOx films. In aqueous KOH electrolyte, EC process and activated state strongly relies on Ni2+ distribution on films surface, while NiOx experiences two phases oxidation to get thorough coloration in PC‐Li based electrolyte.

Novel Prussian White@MnO2-Based Inorganic Electrochromic Energy Storage Devices with Integrated Flexibility, Multicolor, and Long Life

“…Among this, ΔOD refers to the optical density at a given wavelength, and Q is the unit charge density resulting from the coloring process . A good CE meant that the smaller charge quantity can drive the larger optical contrast and mainly depended on darkened coloration.…”

“…(2) Among this, ΔOD refers to the optical density at a given wavelength, and Q is the unit charge density resulting from the coloring process. 48 A good CE meant that the smaller charge quantity can drive the larger optical contrast and mainly depended on darkened coloration. Similarly, the bleached efficiency is the specific value of optical density and unit charge density during the bleaching process.…”

Nickel oxide electrochromic films: mechanisms, preparation methods, and modification strategies–a review

“…22 Notably, a large number of reports have found a significant activation process during the initial very few to hundreds of cycles of NiO in aqueous electrolytes, during which both optical modulation and charge capacity increase significantly. 46,[103][104][105] Such an activation process is believed to be the storage process of Ni(OH) 2 , which also corresponds the hydration of NiO into Ni(OH) 2 . 102,106 Although NiO exhibits high optical modulation and rapid response, the cyclic stability faces severe degradation in aqueous electrolytes (usually o 500 cycles).…”

Flexible Inorganic All-Solid-State Electrochromic Devices toward Visual Energy Storage and Two-Dimensional Color Tunability

“…Although the excellent energy storage function of inorganic ECDs has been verified in most literature, − monotonous color change is also the common phenomenon for most inorganic electrochromic materials or devices. For example, anodic electrochromic material (ECM) NiO only turns transparent from dark brown; cathodic ECM WO 3 changes from dark blue to transparent . This change from dark color to transparent is helpful to realize high optical or lightness contrast but is hard to meet the desire of multicolor transformation in smart display fields.…”