Nickel Phosphide Electrocatalyst Prepared By Pulse Electrodeposition for Proton Exchange Membrane Water Electrolyzer

Abstract

Hydrogen is one of the main attractions for fossil fuels because it has several advantages. Since the combustion products are pure water, hydrogen is free from environmental pollution problems. And raw materials also use water, which is an infinite material on the earth, so there is no risk of exhaustion.One of the ways to make high purity hydrogen is water electrolysis. Of the known elements, platinum is the most active material as an electrocatalyst in the hydrogen evolution reaction (HER). Platinum and platinum group elements have excellent activity, but there are several drawbacks such as low supply stability and high price due to its scarcity.Considering industrial and economic aspects, electrocatalysts based on inexpensive and abundant transition metals such as Nickel, Copper and Molybdenum have been studied. Pure transition metals have weakness of poor activity and stability in HER. Various types of compounds, such as phosphide, carbide, nitride, and chalcogenide, were prepared to compensate for this.In this study, a nanoparticle-type nickel phosphide (np/Ni-P) electroplated on carbon paper (CP) was used as the cathode of HER. When nickel phosphide is fabricated by electrodeposition, metallic nickel is deposited as well as nickel phosphide. If it is used intactly as an electrode catalyst, the performance and life of the catalyst are reduced as metallic nickel is oxidized in the HER process. So, additional leaching process was added to remove the metallic nickel over-plated.In this study, nickel phosphide on nanoparticles with a large surface area was fabricated using a pulsed electroplating method that alternates electroplating and selective leaching. This makes it possible to produce a catalyst having a wider shape than that of which the surface area was electroplated and leached for the same time. In addition, this altenating process makes it possible to greatly reduce the amount of metallic nickel present in the catalyst, so helps increase the intrinsic activity of the catalyst because the proportion of phosphorus in the catalyst increases.The finally produced catalyst was used as a cathode of a proton exchange membrane water electrolyzer (PEMWE) to investigate the results of a single cell, which showed reasonable activity.