Degradation and regeneration mechanisms of NiO protective layers deposited by ALD on photoanodes

Abstract

The degradation mechanisms of ALD-grown NiO protective layers over 1000 h under anodic alkaline conditions are identified and a recovery mechanism is presented.

Facing Seawater Splitting Challenges by Regeneration with Ni−Mo−Fe Bifunctional Electrocatalyst for Hydrogen and Oxygen Evolution

“…After set in working conditions for 24 h in the various electrolytes, significant changes are observed (Figures 3 and S13–S20). In A‐PW and AS‐PW (Figure 3a–d), samples polarized at anodic potentials (1.7 V vs RHE) electrolytes present follicular structures, resembling known oxy‐hydroxide structures for Ni–Fe–OOH [53] . This significant dissolution/re‐electrodeposition and redistribution observed has been previously also reported for nickel iron hydroxides [40,54,55] …”

“…In A-PW and AS-PW (Figure 3a-d), samples polarized at anodic potentials (1.7 V vs RHE) electrolytes present follicular structures, resembling known oxy-hydroxide structures for Ni-Fe-OOH. [53] This significant dissolution/re-electrodeposition and redistribution observed has been previously also reported for nickel iron hydroxides. [40,54,55] Instead, the electrodes polarized at cathodic potentials (À 0.4 V vs RHE) in these two electrolytes present reconfiguration into a nanoparticles-covered surface.…”

Photoelectrochemical water splitting: a road from stable metal oxides to protected thin film solar cells

“…NiO silicon photoanodes protected with 50 nm thick lms grown by ALD at temperatures of 100-300 C, and found to be highly stable over 1000 h but only if periodically depolarized. 286 This reversible degradation mechanism was attributed to higher oxidation states like NiO 2 being formed, being less catalytic and less conductive, but it must be further analysed. Signicant resistance increase at higher than 100 C deposition temperatures was found, together with less defective lms, pointing at a reduction of the p-type behaviour and making the lms more insulator.…”

“…Similar maximum photovoltages for n-Si/p-Si and n + p-Si/p + n-Si PEC electrodes have been obtained by other authors. 140,165,197,202,203,206,212,217,227,235,238,239,286,330 In recent years, several other examples of buried junctions can be found, resembling solar cell structures with other materials. In 2014, Kast et al 232 protected a commercial textured n + p silicon solar cell with 10 nm Ti/50 nm F : SnO 2 /50 nm TiO 2 and 2 nm Ir as HER catalyst to form a photocathode, obtaining onset potentials $0.6 V vs. RHE and >30 mA cm À2 .…”

Atomic Layer Deposition for the Photoelectrochemical Applications

“…Showing the potential to act as a bifunctional coating. Unfortunately the reported photocurrent was low (Ta 2 O 5 , [ 130 ] NiO x , [ 131 ] and ZnO [ 80,132 ] ) or their stability limited (MnO [ 133 ] ). Although a variety of metal oxides can be easily produced by ALD methods ( Table 5 ), also at modest temperatures that are of special interest for the protection of organic semiconductors.…”