This paper reviews the progress in applying the plasma-driven solution electrolysis (PDSE), which is also referred to as the contact glow-discharge electrolysis (CGDE) or plasma electrolysis, for hydrogen production. The physicochemical processes responsible for the formation of PDSE and effects occurring at the discharge electrode in the cathodic and anodic regimes of the PDSE operation are described. The influence of the PDSE process parameters, especially the discharge polarity, magnitude of the applied voltage, type and concentration of the typical electrolytic solutions (K₂CO₃, Na₂CO₃, KOH, NaOH, H₂SO₄), presence of organic additives (CH₃OH, C₂H₅OH, CH₃COOH), temperature of the electrolytic solution, the active length and immersion depth of the discharge electrode into the electrolytic solution, on the energy efficiency (%), energy yield (g(H₂)/kWh), and hydrogen production rate (g(H₂)/h) is presented and discussed. This analysis showed that in the cathodic regime of PDSE, the hydrogen production rate is 33.3 times higher than that in the anodic regime of PDSE, whereas the Faradaic and energy efficiencies are 11 and 12.5 times greater, respectively, than that in the anodic one. It also revealed the energy yield of hydrogen production in the cathodic regime of PDSE in the methanol–water mixture, as the electrolytic solution is 3.9 times greater compared to that of the alkaline electrolysis, 4.1 times greater compared to the polymer electrolyte membrane electrolysis, 2.8 times greater compared to the solid oxide electrolysis, 1.75 times greater than that obtained in the microwave (2.45 GHz) plasma, and 5.8% greater compared to natural gas steam reforming.

Over the past several decades, much attention has been given to the development of technologies utilizing solar energy to generate inexpensive and clean heat for heating purposes of buildings and even for electricity generation in the concentrating solar thermal power (CSTP) plants. However, unlike conventional heatgenerating technologies consuming coal, natural gas, and oil, heat produced by solar energy is intermittent because it is significantly affected by daily (day-night) and seasonal fluctuations in solar insolation. This fact issues a considerable challenge to the adoption of solar energy as one of the main renewable heat sources in the future. Therefore, along with the development of the different solar technologies, the heat storage technologies have also been the focus of attention. Use of the storage devices, able to accumulate heat, enables not only enhance the performance of the heating systems based on solar energy but also make them more reliable. This paper gives an overview of the various sensible heat storage technologies used in tandem with the fluctuating solar heat sources.

The paper presents the results of an experimental study of the exothermal and endothermal effects occurring on the dissolution of potassium nitrate KNO³, ammonium nitrate NH⁴NO³, potassium hydroxide KOH and sodium hydroxide NaOH, in distilled water with natural mixing and forced stirring. It is shown that for natural mixing, NH⁴NO³ and KOH are the most appropriate working substances for cooling and heat generation respectively, while for forced stirring, NH⁴NO³ and NaOH display better performance. The optimal concentrations of the liquid solutions for achieving extreme temperatures and maximal enthalpy changes are also defined. In addition, the regression function and regression coefficients describing correlations between the total enthalpy change of the calorimetric system and the solution concentration are found, for the most suitable liquid solutions. The experimental results obtained can be used to develop generating reactors for exothermal heating and endothermal cooling for a thermochemical seasonal storage system able to store solar heat or heat from combined heat and power (CHP) units of biogas plants in summer, for heating purposes in winter, while generating cooling to support air conditioning systems in summer.

This paper presents results of the experimental study of the plasma discharges in the anodic and cathodic regimes of plasma-driven solution electrolysis (PDSE) in 10 wt% Na2CO3 aqueous solution. The study revealed features of the plasma discharge formation at the smaller electrode and values of the breakdown and discharge onset voltages for the anodic and cathodic regimes of PDSE. By applying the fast Fourier transformation analysis, the frequency characteristics of both plasma discharges were found. In the anodic regime of PDSE, the electrical discharge occurred at much higher frequencies (dozens of kHz), while in the cathodic regime at much lower frequencies (hundreds of Hz) but at higher amplitudes of the discharge current and voltage, resulting in higher electrical power dissipation. The applied optical emission spectroscopy (OES) showed emission lines of the hydroxyl (OH*), hydrogen (H*), and oxygen (O*) radicals formed as a result of the dissociation of the water molecules. The obtained results were discussed in terms of the hydrogen production efficiency by the PDSE method.

In this paper, the results of an experimental study on hydrogen production at a tungsten discharge electrode with negative polarity in the DC electrolysis of a typical 10 wt% Na₂CO₃ aqueous solution in three operational regimes (the Faradaic, transition, and plasma-driven solution electrolysis (PDSE)) are presented for the first time. To focus the study on hydrogen production, a flowing inert gas (argon) was used to transport the gas mixture produced at the discharge electrode and prevent any other potential chemical reactions. The results showed that the highest hydrogen production rate of 0.147 g(H₂)/h was achieved in the cathodic PDSE regime at the applied DC voltage of 198 V. However, the energy yield of hydrogen production of 0.405 g(H₂)/kWh obtained at the applied voltage range of 141–170 V in the PDSE regime was lower than that obtained in the Faradaic regime (0.867 g(H₂)/kWh) at 28 V. The energy balance of hydrogen production in the cathodic PDSE regime for the typical aqueous solution of Na₂CO₃ carried out for the first time showed that a significant share (˃98%) of the electrical energy consumed is spent on heating and evaporation of the electrolytic solution. This explains why the energy yield of hydrogen production is low in the PDSE regime. Because most of the energy is consumed for heat generation in the cathodic PDSE regime, organic liquid hydrogen carriers, such as alcohols, which have a lower boiling temperature, heat of evaporation, and standard Gibbs free energy, should be considered better aqueous electrolytic solutions in terms of the energy yield of hydrogen production in the PDSE regime.