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EP-4741053-A1 - NICKEL-BASED PHOSPHIDE FOR OXYGEN EVOLUTION REACTION IN ALKALINE WATER ELECTROLYSIS USING SODIUM HYPOPHOSPHITE SUBSTITUTION AND PYROLYSIS AND METHOD FOR PREPARATION THEREOF

EP4741053A1EP 4741053 A1EP4741053 A1EP 4741053A1EP-4741053-A1

Abstract

The present disclosure relates to a method for preparing a nickel-based phosphide catalyst for oxygen evolution reaction in alkaline water electrolysis anode using sodium hypophosphite(NaH 2 PO 2 ) substitution and pyrolysis.

Inventors

  • CHAE, GYU SIK
  • KIM, GIL HO
  • KIM, HANSUNG

Assignees

  • Hanwha Solutions Corporation
  • UIF (University Industry Foundation), Yonsei University

Dates

Publication Date
20260513
Application Date
20240807

Claims (12)

  1. A method for preparing a nickel-based phosphide represented by the following Chemical Formula 1, comprising the steps of: dissolving nickel chloride as a first metal, a second metal(M) chloride, and sodium hypophosphite(NaH 2 PO 2 ) in water (step 1); evaporating a solvent to obtain a nickel phosphide precursor and second metal phosphide precursor mixture (step 2); pyrolyzing the nickel phosphide precursor and second metal phosphide precursor mixture to obtain a composition containing a nickel-based phosphide (step 3); and washing the composition with water to obtain a nickel-based phosphide (step 4): [Chemical Formula 1] NiM x P y wherein x is 0.01 to 0.15, y is 0.5 to 1.2, and M is one or more selected from the group consisting of Fe, Mo, Co, Mn, Cu, Zn, Cr, and V.
  2. The method for preparing a nickel-based phosphide according to claim 1, wherein: after the step 1, the method further comprises adding a solvent to the solution of nickel chloride, second metal(M) chloride and sodium hypophosphite dissolved in water to recrystallize sodium chloride(NaCl).
  3. The method for preparing a nickel-based phosphide according to claim 1, wherein: the nickel phosphide precursor is nickel hypophosphite, and the second metal phosphide precursor is a second metal hypophosphite.
  4. The method for preparing a nickel-based phosphide according to claim 1, wherein: in the step 1, sodium hypophosphite is mixed at 200 to 300 mol parts per 100 mol parts of the nickel chloride and the second metal chloride.
  5. The method for preparing a nickel-based phosphide according to claim 1, wherein: the second metal(M) is Fe.
  6. The method for preparing a nickel-based phosphide according to claim 1, wherein: in the (step 1), the mixing ratio of the nickel chloride and the second metal chloride is 30 mol parts to 300 mol parts of the second metal chloride per 100 mol parts of the nickel chloride.
  7. The method for preparing a nickel-based phosphide according to claim 1, wherein: in the (step 4), the pyrolysis temperature is 250 to 500°C.
  8. The method for preparing a nickel-based phosphide according to claim 2, wherein: the solvent is ethanol.
  9. The method for preparing a nickel-based phosphide according to claim 1, wherein: in the (step 5), a pyrolysis byproducts and a second metal in the composition containing the nickel-based phosphide are removed.
  10. The method for preparing a nickel-based phosphide according to claim 1, wherein: the water in the (step 1) to (step 2) or (step 4) is deionized water
  11. A nickel-based phosphide represented by the following Chemical Formula 1 and having a BET surface area of 10 m 2 /g or more: [Chemical Formula 1] NiM x P y wherein x is 0.01 to 0.15, y is 0.5 to 1.2, and M is one or more selected from the group consisting of Fe, Mo, Co, Mn, Cu, Zn, Cr, and V.
  12. An alkaline water electrolysis system comprising the nickel-based phosphide according to claim 11 as an anode catalyst.

Description

[TECHNICAL FIELD] CROSS-REFERENCE TO RELATED APPLICATION(S) This application claims the benefit of Korean Patent Application No. 10-2023-0104171 filed on August 9, 2023 with the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference in its entirety. The present disclosure relates to a nickel-based phosphide catalyst using sodium hypophosphite(NaH2PO2) substitution and pyrolysis and a method for preparation thereof, and more particularly, to a highly active non-precious metal phosphide catalyst for oxygen evolution reaction in alkaline water electrolysis anode that reduces the amount of phosphorus precursor used, does not use precious metals, and can achieve mass production, and a method for preparation thereof. [BACKGROUND] Hydrogen energy is attracting attention as an alternative environmentally friendly energy for fossil fuels in that it is abundant in resources and does not emit harmful substances. Alkaline water electrolysis, which is one of the methods for producing hydrogen, is less expensive than polymer electrolyte membrane and solid oxide water electrolysis and is suitable for mass production. The oxygen generation electrode has the greatest impact on the reaction rate in alkaline water electrolysis. The oxygen evolution reaction(OER) in alkaline electrolytes generates O2 through a four-electron reaction via four OH-, and therefore has a slow reaction rate relative to the hydrogen evolution reaction. Due to the complex reaction mechanism and slow reaction rate, a high overpotential occurs at the OER electrode, which becomes a major reason why alkaline electrolysis has a low efficiency. Therefore, using a catalyst having low overpotential for the OER reaction in the alkaline water electrolysis cells is essential to increase cell and stack efficiency. OER electrochemical catalysts for alkaline water electrolysis are known that precious metal oxide catalysts such as IrO2 and RuO2 show excellent OER performance. However, since Ir and Ru are expensive and limiting noble metals, the development of non-precious metal catalysts to replace them is necessary. Alkaline water electrolysis can use relatively inexpensive transition metals such as Ni, Fe, and Co as catalyst materials unlike acidic environments. Among them, Ni is known to have excellent electrochemical reaction rate and corrosion resistance in alkaline solutions, and is easily alloyed with other metals, and thus Ni-based alloy catalysts are being actively studied. As a method for preparing Ni-based OER catalysts, studies trying to lower the Tafel slope by doping Ni with non-metallic elements such as O, P, N, S, and Se are being actively advanced. It has been reported that Ni2P, NiCo2O3, Ni3Se2, and the like have similar Tafel slopes to RuO2 and IrO2 in the oxygen evolution reaction. Among non-metallic elements, nickel phosphide(NiP) catalysts utilizing P have a core (phosphide)-shell (oxide) structure in which phosphide on the catalyst surface is eluted in the OER measurement process. Such a core-shell structure is known to have excellent catalytic activity and durability because it improves OER performance through the oxide in the shell, and the phosphide in the core can compensate for the insufficient electrical conductivity of the shell. In order to further improve the performance of such NiP catalysts, methods of preparing or doping dissimilar alloys by introducing a second metal are being actively studied. Many papers have reported that NiCoP, NiFeP and NiFeCoP catalysts, which are produced by alloying two types or more, have higher OER performance than single-metal phosphides of NiP, CoP, and FeP. It has also been reported that when Fe is doped in NiCoP, the Fe optimizes the electronic structure and improves OER performance. However, the method most widely used in the preparation of such metal phosphides is a chemical vapor deposition(CVD) method. The CVD method is a method for preparing phosphides by generating hydrogen phosphide(PH3) at high temperatures using sodium hypophosphite(NaH2PO2) as a phosphorus precursor, and is most widely used in the preparation of phosphides. However, the CVD method heat-treats NaH2PO2 while being separated from the metal precursor, which results in poor contact between the metal and PH3. Therefore, the metal precursor and NaH2PO2 are added at a mass ratio of 1:5 to 20 to prepare a metal phosphide. This CVD method is disadvantageous for mass production because not only it is an uneconomical method that uses an excessive amount of phosphorus precursor, but also the contact between the PH3 generated from the phosphorus precursor and the metal precursor is low. Another method utilized in the preparation of metal phosphides is an electroplating method, which requires a substrate such as Ni foam as a substrate for plating. This electroplating method is a simple catalyst production method, but it is difficult to produce a powder-type catalyst, and therefore is not suitable