Print-Light-Synthesis of Ni and NiFe-nanoscale catalysts for oxygen evolution

By hyphenating inkjet printing and flash light irradiation, Ni- and NiFe-nano-electrocatalysts of diameters below 2.5 nm with ultralow loadings below 2 µg·cm–2 are synthesized. To achieve this, nanoliter ink volumes containing Ni and Fe chlorides as catalyst precursors are rapidly printed on large-scale carbon nanotube-coated glassy carbon electrodes and exposed to millisecond-long high intensity light pulses from a Xenon flash lamp. The carbon nanotube coating acts as light-to-heat absorber generating surface peak temperatures of several hundred degrees. The light-induced reduction of the Ni and Fe precursors into chloride-free mixed metal composites is facilitated by alcohols that act as sacrificial electron donors in the printed precursor films. Besides the merging of large-scale electrode production and nanoparticle synthesis into a single robust and rapid process, the adjustability of the precursor ratios using parallel printheads, the operation under ambient conditions, the absence of capping agents as well as surfactants, and the up-scalability to industrial levels are the major advantages of this new electrode fabrication method. Furthermore, the process is superior to standard lab-scale electrocatalyst deposition methods, such as drop casting, and is more flexible to control compared to hydro- and solvothermal syntheses. The electrochemical characterisation of the Ni- and NiFe-based nano-electrocatalysts by voltammetric cycling leads to onset potentials as low as 240 mV (at 0.1 mA·cm–2), overpotentials of 334 mV (at 10 mA·cm–2), Tafel slopes of 41 mV·dec–1 and high turnover frequencies of up to 4.5 s–1 for the oxygen evolution reaction.