**4. Conclusions**

This work firstly focuses on the effect of different thickness Ni foam anodes on the performance of alkaline direct ethanol fuel cells. The result exhibited that among the 0.3 mm, 0.6 mm, and 1.0 mm thickness Ni foam electrodes, the 0.6 mm thick electrode had the best cell performance, reaching a maximum power density of 56.3 mW cm−2 at 60°C, 2.4 times higher than that of 0.3 mm and 1.8 times of that of 1.0 mm. The reason was that the 0.3 mm Ni foam was thin, the catalyst was prone to aggregate on the electrode surface, and was unevenly distributed in the threedimensional space, leading to the increase of electrochemical reaction resistance

*Nickel Foam Electrode with Low Catalyst Loading and High Performance for Alkaline Direct… DOI: http://dx.doi.org/10.5772/intechopen.100287*

and the decrease of performance. On the other hand, the electron and mass transfer channel of Ni foam with a thickness of 1.0 mm was long, which caused larger polarization. These results have been proven by SEM image, polarization curve test, EIS test, and CV test. It is necessary to optimize the thickness of the Ni foam to more effectively use the catalyst, balance the resistance of electron conduction and mass transfer, and improve the cell performance.

Secondly, the mixed acids etching method is applied to pretreat the Ni foam. It is found that etching can obtain porous skeleton surface, since the strong oxidizing and corrosive nature of the mixed acids can quickly consume the metallic nickel, leaving many micro-holes on the skeleton surface. Using the three-electrode system, it is concluded that the Pd/Ni foam electrode pretreated with mixed acids has a larger ECSA and higher ethanol oxidation activity than HCl. A mixed acid treated Ni foam anode with low Pd loading (0.35 mg cm−2) is prepared by simply soaking three times for ADEFC performance testing. The peak power density reaches 30 mW cm−2, which is double the performance of the HCl treated anode. The performance improvement is attributed to the micro-holes produced by mixed acids etching, which enhance the roughness of the skeleton and improve the ECSA of the catalyst. This work opens a new platform for in-depth exploration on metal foam electrodes.

## **Acknowledgements**

The work described in this chapter was fully supported by Grants from the NSFC, China (No. 51676092), State Key Laboratory of Engine at Tianjin University (No. K2020-14), Six-Talent-Peaks Project in Jiangsu Province (No. 2016-XNY-015), and High-Tech Research Key Laboratory of Zhenjiang City (No. SS2018002).

### **Conflict of interest**

The authors declare no conflict of interest.
