Oxygen evolution on Fe-doped NiO electrocatalysts deposited via microplasma

Abstract

The oxygen evolution reaction (OER) in alkaline media was investigated on nanostructured FeO, NiO, and NiFeO (Fe-doped, rocksalt NiO, x = 0.05-0.19) electrocatalysts deposited via microplasma on indium tin oxide. A detailed investigation of film morphology, structure, and chemical surface state using SEM, XRD, and XPS, respectively, was carried out to understand catalytic activity, which was assessed using cyclic voltammetry and chronopotentiometry. Iron was seen to be fully incorporated into the parent rocksalt NiO lattice during microplasma deposition, and overpotentials (η) decreased from 360 mV for NiO to 310 mV for NiFeO at 10 mA cm. Interestingly, overpotential did not change significantly for Fe compositions from 5-19%. The NiFeO films displayed relatively low Tafel slopes of 20-30 mV dec at 0.01-1 mA cm, demonstrating their high activity for (OER). Turn-over-frequency (TOF, i.e., O molecules per Ni atom per s) at η = 350 mV revealed a continuous improvement in activity of the NiO surface with increasing Fe content, where values of 0.07 and 0.48 s were measured for undoped NiO and NiFeO films, respectively. Chronopotentiometry measurements followed by SEM and XPS verified that the as-deposited NiFeO catalysts were mechanically and chemically stable for OER under alkaline conditions. This work highlights that microplasma-based deposition is a general approach to realize conformal coatings of nanostructured, doped oxides with high activity for OER.

Microplasmas for Advanced Materials and Devices

“…Recently, a versatile microplasma‐based approach ( Figure ) has been demonstrated for direct deposition of crystalline MONS including α‐Fe 2 O 3 , CuO, NiO, and Fe‐doped NiO on different substrates including polymeric materials, conductors, insulators, fibers, and patterned substrates at ambient temperature (Figure a) . The as‐prepared CuO films were used as active electrodes for lithium ion batteries, exhibiting high specific capacity and good electrochemical responses over a large number of voltage sweep cycles (Figure b).…”

Multiscale Plasma‐Catalytic On‐Surface Assembly

“…Metal-reduction-based on-surface plasma printing has shown great promise at atmospheric pressure. [39][40][41] In this method, a precursor deposited in selected physical locations is reduced to form a desired product, producing patterned regions with varied chemistry. It is also possible to use inkjet printing to introduce a metal precursor, followed by the application of a plasma for reduction of the precursor.…”

“…The nanocrystals can be integrated into various electronic, optoelectronic, and other devices. [41] Catalyst synthesis and activation has also been demonstrated through atmospheric plasma processing, with smaller particle size and a more controllable structure than traditional thermal means, and could also be incorporated into the numerous options for multiscale on-surface assembly. [47] In the example presented in Figure 3f, plasma-generated reactive oxygen species generated in a dielectric barrier discharge in air effectively modify oxidation states of Fe and Co metallic catalytic sites in the Prussian blue analog based metalorganic frameworks.…”

Modeling magnetic evolution and exchange hardening in disordered magnets: The example of Mn1−xFexRu2Sn Heusler alloys

“…Magnetic exchange hardening, a phenomenon that increases a material's resistance to demagnetization, typically occurs in two-phase mixtures consisting of a ferromagnetic (FM) phase and an antiferromagnetic (AFM) phase. [1][2][3] It is well established that magnetic hardening can emerge from magnetic interactions across the interfaces separating the FM and the AFM phases, which becomes especially pronounced in nano-structured twophase mixtures. Less understood is the anomalous exchange hardening observed in the chemically disordered, single phase Heusler alloys Mn 1−x Fe x Ru 2 Sn and Mn 1−x Fe x Ru 2 Ge.…”