Title : Structural and electrochemical study of IrO2 and NiO coated Ni Anode by atomic layer deposition (ALD)
Atomic Layer Deposition (ALD) is a special type of Chemical Vapor Deposition (CVD) technique that could grow conformal and uniform thin films on the surface of a substrate through alternate self-limiting surface reactions. The development of this technique has been successfully demonstrated in thin film electroluminescent display production, but the industrial use of this technique remained marginal for more than two decades.1 On the other hand, hydrogen is one of the promising solutions for the sustainable and green energy problem, but the process is still not optimal because of the sluggish kinetic of the anodic oxygen evolution reaction (OER) due to the well-known scaling relation restriction.2 In this study, iridium dioxide (IrO2) and nickel oxide (NiO) thin films were deposited on industrial Ni coarse mesh (and Si  for reference) as an anode for alkaline water electrolysis. ALD operating parameters such as the number of deposition cycles, amount of O3 flow, deposition and sublimation temperatures, and pulse and purge rates were varied to determine the effect of changing these parameters on the electrochemical performance of the material. Total deposition time took approximately 14 hours (for 1000 cycles) and 21 hours (for 1500 cycles).
To establish the structure-catalytic behavior relationship, materials were characterized using: Grazing Incidence X-ray Diffraction (GIXRD), X-ray Reflectivity (XRR), Scanning Electron Microscopy (SEM), and iR-corrected Single Electrode Potential Test (CISEP). As seen on the GIXRD patterns (Figure 1a), variation on the operating parameters did not affect the crystalline phases of IrO2 (tetragonal) and NiO (cubic) present on the thin films. OER was investigated in industrial conditions (high temperature and high KOH solution) at varying high current densities of 1 to 12 kA/m2). Results from the electrochemical tests (Figure 1b) showed the catalytic activity of IrO2 and NiO thin film (approx. 25 to 60 nm). Overpotential values, η, of the coated Ni mesh were 20 to 60 mV lower than the uncoated Ni mesh. In summary, the study has demonstrated the feasibility of using ALD technique to deposit conformal, uniform and electroactive thin films on industrial metallic substrates as an anode for alkaline water electrolysis.