NiFe foam as electrocatalyst after hard anodizing

In a recent article published in the magazine ACS Applied Energy MaterialsIn this article, the researchers discussed the development of an efficient and stable electrode for the oxygen evolution reaction (OER) through anodizing of NiFe foam.

Stady: NiFe foam anodizing: efficient and stable electrode for oxygen evolution reaction. Image Credit: Party people studio / Shutterstock.com

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Fossil fuels are scarce, and their damage to the environment makes it imperative for people to use clean and sustainable energy sources. A promising method for storing various energy sources is the splitting of water to form molecular hydrogen on a large scale.

However, the bottleneck for water splitting is OER through the water oxidation reaction. Ru4 and Ir5 compounds are effective catalysts for OER, but they are expensive and rare for widespread use. The high costs of Ru and Ir are not the main problems due to weak IrO2– or RuO2Based stimuli are easily accessible and inexpensive. However, due to its rarity in the earth’s crust, it must be replenished.

NiFe (hydr) oxides as well as OER catalysts work in alkaline solutions. NiFe and other metal oxides (hydr) were synthesized toward OER using a variety of techniques. According to certain studies, enhancing contact with metallic metal oxide can significantly increase the catalytic activity. The interfaces created between metals and metal oxides are useful for stress production, electron transfer, modulation of oxygen uptake energy, and transfer of electrons to metal oxides.

About the study

In this study, the authors discuss the development of NiFe foam as an efficient and stable electrocatalyst after intense anodizing at 60 V in a bipolar system. Several techniques have been used to characterize the NiFe oxide formed on the surface of the NiFe foam. These techniques demonstrated the presence of various NiFe (hydr) oxides on the surface of NiFe foam, including NiO, Ni(OH)2and NiO(OH).

The team showed that the starting OER overvoltage was 220 millivolts for an electrode prepared in a KOH solution (1.0 M). Overcapacity of 1, 10 and 100 mA/cm2 Activities are observed, respectively, 290, 346 and 500 mV. The bare foam was protected from further oxidation by a stable NiFe oxide layer resulting in a stable OER electrocatalyst.

The researchers used anodizing as a quick and easy way to create a surface from nanostructured NiFe foam using NiFe (hydr) oxide. The ratio of iron to nickel was 1:50, which was low enough to prevent the formation of a large amount of iron oxide. However, the ratio was large enough to prevent iron depletion on the surface of the oxidized NiFe foam. An increase in iron oxide synthesis or a significant decrease in iron led to a decrease in the OER of NiFe(hydr) oxide.

Notes

OER moved rapidly at a current density of 50 mA/cm2, and gas bubbles developed without significantly accumulating on the electrode surface. At overvoltages of 290, 346, and 500 mV, respectively, the current densities are 1, 10, and 100 mA/cm2 seen. Inductively coupled plasma mass spectrometry (ICP-MS) showed that neither Fe nor Ni were found in the electrolyte after 10 h of time mixing measurement at 1.61 eV. The total specific surfaces of the new and anodized electrodes were calculated, according to the Brunauer, Emmett, and Teller (BET) method to be 3.7 and 10.3 m2.g-1Straight.

The pore sizes of the new and oxidized electrodes ranged from 3.2 to 30 nm. A new NiFe foam measured by temporal analysis at 1.61 V has a current density of 11.4 mA/cm2which increased to 17.9 mA/cm2 When the solution has been stirred. Without stirring, current density 17mA/cm2 Viewed for 24 hours. The oxygen metric experiment was combined with timing measurement, and the advanced oxygen of the oxidized NiFe foam was directly sensed using fluorescence. This showed Faradaic efficiency of 75% for the first 500 seconds, but more than 90% after that.

The Tafel plot for the oxidized electrode at pH 14 showed that log(j) against the overvoltage was linear, with a slope of 56.8 mV per decade. According to corrected cyclic voltammetry plots based on electrochemical active surface area (ECSA) or BET methods, the number of active sites increased rather than the amount of activity at each site of the oxidized foam. However, at a lower overvoltage in the range 220–250 mV, the modified CVs based on both BET and ECSA showed higher activity of the oxidized electrode compared to the fresh foam due to the higher iron concentration on the surface of the oxidized electrode compared to the fresh electrode. electrode.

Conclusions

In conclusion, this study demonstrated that creating reliable and effective OER catalysts is essential to bring green energy technology to market. Using anodizing, in a simple one-step process, nanostructured NiFe oxides were formed on the surface of the NiFe foam.

NiFe oxide was characterized using several techniques, which showed that a variety of NiFe oxides were produced during the oxidation process.

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references

Hashemi, N.; , Nandi, S. , Chai, KH, et al. Anodizing NiFe foam: an efficient and stable electrode for the oxygen evolution reaction. ACS Applied Energy Materials, (2022). https://pubs.acs.org/doi/10.1021/acsaem.2c01707

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