## 3 Results and Discussion  
### Cyclic Voltammetry  
Figure 1 presents cyclic voltammograms recorded for the HER on the polycrystalline nickel electrode surface, over the potential range from \(-\)0.60 to 0.20 V vs. RHE. Hence, the current density recorded at the potential of \(-\)0.60 V for the unmodified NaOH solution approached \(-\)7.0 mA cm\({}^{-2}\) (see red plot in Figure 1). Then, the introduction of acetone into the electrolyte resulted in a considerable increase in the respective current density parameter, reaching ca. \(-\)7.5 and \(-\)7.75 mA cm\({}^{-2}\) (current density amplification by ca. 1.07 and 1.11 times) for acetone concentrations of 1.0 \(\times\) 10\({}^{-3}\) and 1.0 \(\times\) 10\({}^{-5}\) M, respectively. The above could be considered in terms of significantly more hydrogen molecules being generated compared with acetone-free sodium hydroxide solution.  
As the authors of this work argued in their recently published article (see Scheme 2 in [16]), the facilitation of the HER rates is believed to result from a considerable reduction in the surface tension parameter, caused by acetone-to-water hydrogen bonding interactions [14; 15], leading to a significantly diminished overall reaction overpotential.  
The oxygen evolution reaction was examined over the potential range from 0.00 to 1.70 V (see Figure 2). Thus, a cyclic voltammetry profile recorded on the polycrystalline Ni electrode in acetone-free 0.1 M NaOH solution exhibits an anodic peak centred at  
Figure 1: The cyclic voltammograms recorded on the surface of polycrystalline Ni electrode (at 50 mV s\({}^{-1}\), on the second cycle), within the potential range for HER in 0.1 M NaOH electrolyte, in the absence and presence of acetone, at the indicated (CH\({}_{3}\))\({}_{2}\)C=O concentrations.  
ca. 1.55 V, which illustrates the process of \(\beta\)-NiOOH formation from Ni(OH)\({}_{2}\). Hence, a cathodic reduction feature, centred at about 1.35 V corresponds to the reduction of nickel oxyhydroxide, later on the Ni electrode surface [18; 19; 20]. Extending the anodic sweep beyond 1.60 V vs. RHE results in a pronounced increase of the anodic current, which signifies the initiation of the oxygen evolution reaction. The introduction of acetone notably alters both the redox features and the OER current response. Thus, both anodic and cathodic peak currents become more pronounced, and slight shifts in the peak positions are also observed. Moreover, for the OER activity region, a significant rise in the recorded voltammetric current density values is observed to reach, at the maximum of electrode potential (1.70 V), about 3.05 and 3.55 mA cm\({}^{-2}\), respectively, at the acetone concentrations of 1.0 \(\times\) 10\({}^{-3}\), and 1.0 \(\times\) 10\({}^{-5}\) M (compared with ca. 2.55 mA cm\({}^{-2}\) for the unmodified electrolyte, see Figure 2 again). The OER current density enhancement could be attributed to the reduced surface tension of the electrolyte, due to acetone-water hydrogen bonding interactions, which eventually results in the facilitation of the gas bubble detachment process. On the other hand, acetone is prone to undergo surface adsorption and further quasi-reversible electro-oxidation phenomenon (proceeding in line with the process of \(\beta\)-NiOOH formation), prior to the onset of the oxygen evolution reaction [14; 15]. The latter results in significantly rising voltammetric anodic and cathodic charges for the lowest and intermediate acetone concentrations, whereas the highest (CH\({}_{3}\))\({}_{2}\)C=O concentration (1 \(\times\) 10\({}^{-3}\) M) already starts contributing to the surface poisoning effect (see Figure 2). In addition, acetone, due to its molecular structure, exhibits higher polarizability than water molecules at the interface and, as such, might contribute to the increased values of the recorded interfacial capacitance [21; 22].