Optimization of Integrated Electrodes Using Laser-Made Bimetallic Nanocatalysts

The research aimed to immobilize laser-made [NiFe]-layered double hydroxide nanocatalysts on
hydrophilic carbon fiber paper with uniform nanoparticle distribution. These bimetallic
nanomaterials are excellent electrooxidation catalysts, 1 and we chose laser-made [NiFe]-layered
double hydroxide nanocatalysts 2 because the laser synthesis is surfactant-free. 3 We used
hydrophilic carbon fiber paper as an electrode support due to its high surface area, conductivity,
cost-effectiveness, durability, and scalability. 4 To maintain hydrophilicity, we employed a rapid
green chemistry process developed by the Müller group. 4 Uniform nanoparticle distribution on
the carbon fiber paper was achieved using aqueous citrate-capped gold colloid immersion. 5
However, laser-made [NiFe]-layered double hydroxide nanoparticles aggregate in aqueous
suspension, posing challenges for uniform distribution in integrated electrodes. To address this,
we systematically explored various surfactants, a dispersant, and sonication methods to load
these nanoparticles onto the carbon fiber paper with minimal aggregation while retaining
adhesion of nanoparticles on the carbon. We kept catalyst mass constant and tested citrate,
CTAB, SDS, and Triton-X with different concentrations as surfactants, applied different volumes
of isopropanol as a dispersant to surfactant-free suspensions, and used a sonication bath or
sonication horn with varying times. We analyzed nanoparticle distribution by scanning electron
microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) mapping. SEM provided
insights into nanoparticle aggregation, while EDX mapping provided relative catalyst amounts
on carbon surfaces. In summary, our study demonstrates the successful adhesion of nanocatalysts
to integrated electrodes with minimized aggregation using a combination of methods.

References:
1) B.M. Hunter, H.B. Gray, A.M. Müller, Earth-Abundant Heterogeneous Water Oxidation
Catalysts. Chem. Rev. 2016, 116, 14120-14136.
2) B.M. Hunter, J.D. Blakemore, M. Deimund, H.B. Gray, J.R. Winkler, A.M. Müller, Highly
Active Mixed-Metal Nanosheet Water Oxidation Catalysts Made by Pulsed-Laser Ablation in
Liquids. J. Am. Chem. Soc. 2014, 136, 13118-13121.
3) R.C. Forsythe, C.P. Cox, M.K. Wilsey, A.M. Müller, Pulsed Laser in Liquids Made
Nanomaterials for Catalysis. Chem. Rev. 2021, 121, 7568-7637.
4) M.K. Wilsey, K.R. Watson, O.C. Fasusi, B.P. Yegela, C.P. Cox, P.R. Raffaelle, L. Cai, A.M.
Müller, Selective Hydroxylation of Carbon Fiber Paper for Long-Lasting Hydrophilicity by a
Green Chemistry Process. Adv. Mater. Interfaces 2023, 10, 2201684.
5) R.C. Forsythe, C.P. Cox, M.K. Wilsey, W. Yu, A.M. Müller, High surface area assemblies of
gold nanoparticles on hydrophilic carbon fiber paper with ionomer overlayers for aqueous CO2
reduction electrocatalysis to clean syngas. Top. Catal. 2023, 1-19.