Water Splitting Electrodes Based on Nife Alloy Foil Produced By Roll-to-Roll Processing
Authors: Park Hoon Kee , Lee Mi Gyoung , Jang Ho Won 
Published: February 2020

With the rapid increase of global temperature and depletion of fossil fuels, developing sustainable energy resources is crucial nowadays. Among the various renewable energy source generation approaches, water splitting has attracted increasing attention for clean energy generation and efficient energy storage. Electrochemical production of hydrogen from solar electricity is also an attractive option for generating energy in the form of a hydrogen which could be used at a later stage for electricity. Over the past decades, despite of significant achievements have been obtained, the solar-to-hydrogen (STH) efficiency is still too low for practical applications. Low solar to hydrogen (STH) conversion efficiency is due to the suppressed water splitting reactions by high overpotential, especially oxygen evolution reaction. Due to relatively high overpotential than hydrogen evolution reaction(HER), the oxygen evolution reaction(OER) is a key reaction in water splitting. To overcome this problem, current studies are focused on development of efficient, abundant and inexpensive OER catalyst.
The implementation of efficient electrocatalyst leads to decreased overpotentials, thereby making the whole process more energy-efficiently. Currently, the most efficient catalysts for water splitting are noble-metal catalysts such as Pt-group metals, Ru and Ir-based compounds. Unfortunately, the scarcity and high cost of noble metals seriously impede its large-scale applications in electrocatalytic water splitting. It is therefore highly attractive to explore earth-abundant materials to overcome this obstacle. In past decades, Ni has emerged as an important non-noble metal due to its catalytic power for water splitting and Ni-based compounds have been intensively studied as efficient OER and HER catalysts. Among the various type of Ni based materials, layered transition-metal alloy with Fe have attracted much attention of researchers because of their special redox character and good accessibility for the reaction species. Bimetallic electrocatalysts also have attracted increasing attention as a reliable approach to enhanced electrocatalytic activity for the HER. In the meantime, inspired by the abundant element Ni used in nature, various Ni-based catalysts have been designed to catalyze the conversion of H2O to H2 in commercial alkaline electrolyzers. Among these, Ni–Mo alloys are well-known non-precious-metal electrocatalysts for hydrogen production in alkaline electrolytes because of the increased intrinsic electrocatalytic caused by appropriate binding energy to hydrogen activity compared to pure Ni.
Herein we report an approach to improve efficiency of water splitting electrodes based on flexible NiFe-based foil. Anodic oxidation method is applied to enhance the oxygen evolution activity of NiFe alloy foil. The anodized NiFe alloy foil exhibit significant higher activity than the corresponding Ni foam in base conditions. The anodic oxidation method generate NiFe oxide and hydroxide layers on NiFe alloy surface, act as electrocatalyst. Spontaneously, the anodic oxidation method widen the specific surface area of water splitting electrodes. Increased reaction sites and catalytic behavior of NiFe hydroxide is the reason of improved water splitting property. Because Ni based alloy like NiMo is remarkable hydrogen evolution catalyst, similar to noble metal, electrodeposition method is applied to enhance the hydrogen evolution activity of NiFe alloy foil. NiMo electrodeposited NiFe alloy foil exhibit highly enhanced activity than pure NiFe foil. Combining with 23% Si based solar cell using anodized NiFe alloy foil as anode and electrodeposited NiMo as cathode, PV-EC cell shows excellent STH properties around 18%.