Controlled Synthesis of Transition Metal Oxide Mesocrystals on Graphene Oxide and the Application in Electrocatalysis

• Applicant: Professor Dr. Helmut Cölfen (†)
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Physical Chemistry of Molecules, Liquids and Interfaces, Biophysical Chemistry
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 337373595

• Final Report Year: 2022

Final Report Abstract

This project aimed to investigate the potential of non-precious metal oxide/graphene mesocrystals on HOPG as fuel cells catalysts. First, nickel-iron hexacyanide nanocubes with low polydispersity could be synthesized and used as a precursor of the mesocrystal building blocks. Two synthetic pathways have been designed for the formation of such mesocrystals. In the first pathway, anionic and cationic perylene derivatives have been used as anchored molecules. However, either the shape or the position of the anchored nanoparticles was found to be unfavorable for the formation of monocrystals. The second pathway, which alternates the deposition of the nanoparticles by dip coating and rGO by spray coating could enable reaching a high coverage of nanoparticles with small, organized domains. However, the catalytic activity of such a sample toward OER was comparable to the one of the non-assembled nanoparticles. Through the experimental work, the reshaping of the nanocubes into nickel-iron nanoframes with a large surface-over-volume ratio could be revealed. Although the reshaping mechanism is not fully understood up to now, this new morphology is promising to exhibit a higher catalytic activity as such particles have a higher surface-to-volume ratio than the nanocubes. Due to the setbacks during the first half of this projct and the immediate effects of the pandemic on personal and technical challenges, the focus of this project was changed to hydroxide/carbon black from graphene oxide/GO, in the second part of this work. Hydroxides such as FeNi-layered Double Hydroxide (LDH) are one of the most effective electrocatalysts for OER in alkaline media. Carbon black was chosen as an alternative substrate for improving the electrical conductivity of electrocatalysts as it combines the advantages of low-cost and good electrically conductive ability. In this regard, four reaction routes were developed in an effort to first investigate the formation mechanism of FeNi-LDH and then identify a synthesis route to successfully fabricate FeNi-LDH in water at ambient temperature without using any additives. Evaluation of the OER performance of the resulting products shows that a FeNi-LDH nanocomposite with an optimal composition and ratio could be obtained which exhibits an unprecedentedly high OER activity with an overpotential of 203 mV at 10 mA cm-2. These values outperform commercial RuO2 catalysts as well as the majority of previously reported electrocatalysts. This not only provides valuable references for improving the synthesis condition of LDH, but also opens up a new avenue for producing high-performance OER electrocatalysts in a simple, low-cost, and environmentally friendly manner.

Publications

• New Horizons of Nonclassical Crystallization. J. Am. Chem. Soc., 2019, 141 (26), 10120-10136
  M. Jehannin, A. Rao, H. Cölfen
  
• Synthesis of ultrathin metal oxide and hydroxide nanosheets using formamide in water at room temperature. CrystEngComm., 2021, 23, 3794-3801
  Z.K. Chen, M.H. Huang, H. Cölfen
  
• Synthesis of hierarchical transition metal oxyhydroxides in aqueous solution at ambient temperature and their application as OER electrocatalysts. Journal of Energy Chemistry, 2022, 71, 89-97
  Z.K. Chen, XingkunWang, Sascha Keßler, QiqiFan, M.H. Huang, H. Cölfen
  
• Synthesis of two-Dimensional layered double hydroxide: A systematic overview. CrystEngComm, 2022,24, 4639-4655
  Z.K. Chen, M.H. Huang, H. Cölfen