Nickel electrodes prepared through electrodeposition processes have been demonstrated as promising catalysts for urea electrolysis, towards the applications of urea removal from urea-rich wastewater and hydrogen production.[1-5] The urea electrochemical oxidation process in alkaline media can be described as the equations below:

CO(NH₂)_2(aq) + 6OH⁻ → N_2(g) +5H₂O_(l) +CO_2(g) +6e⁻      (1)

6H₂O_(l) + 6e⁻→3H_2(g) +6OH⁻_(aq)                                       (2)

Reaction (1) and (2) happen at the anode and cathode of the urea electrolyzer respectively.[5] The overall reaction is shown below:

CO(NH₂)_2(aq) +H₂O_(l)→N_2(g) +3H_2(g) +CO_2(g)                   (3)

However, there is still lack of knowledge on how the nickel catalysts behave during the electrodeposition and urea electrolysis process.

Recent development of in-situ transmission electron microscopy (TEM) with liquid cell has provided an excellent tool to direct observe material evolution at nanoscale in a liquid environment.[6] With this technique, sample behavior under dynamic operating conditions, such as various electrochemical reactions with the help of incorporated three-electrodes setup, can be imaged in the real time, which could further assist the understanding of the reaction process along with the mechanism behind it.

Within this study, the nickel electrodeposition process has been investigated using in-situ liquid-cell TEM. The experiments were carried out with a state-of-the-art flow cell TEM holder equipped of three electrodes system. The nickel particles were electrodeposited on a thin glassy carbon working electrode during the cyclic voltammetry (CV) scans, as shown in Figure 1.  The TEM images were recorded using JEM 2100F field emission TEM. This work revealed the formation process of the nickel particles and made it possible to achieve the precise control of electrode synthesis. It also opened a window for understanding other electrodeposition processes and urea electrolysis with nickel based catalysts.

Figure 1 shows the TEM image of electrodeposited nickel particles on the platinum working electrode of the in situ TEM cell along with the cyclic voltammgraphs (inserted) to obtain these nickel particles.

References

[1]   B. K. Boggs, R. L. King, G. G. Botte, Chem. Commun. 2009, 32, 4859-4861

[2]   A. N. Rollinson, J. Jones, V. Dupont, M. V. Twigg, Energy Environ. Sci. 2011, 4(4), 1216-1224

[3]   D. Wang, W. Yan, S. H. Vijapur, G. G. Botte, J. Power Sources 2012, 217, 498-502

[4]   W. Yan, D. Wang, G. G. Botte, Electrochim. Acta 2012, 61, 25-30.

[5]   D. Wang, G. G. Botte, ECS Electrochem. Lett. 2014, 3(9), H29-H32

[6]   H. Liao, K. Niu, H. Zheng, Chem. Commun., 2013, 49, 11720-11727

Figure 1 TEM image of nickel particles with inserted CV curves for electrodeposition.