Hydrogen Production by Water Electrolysis - Factors Affecting Electrolysis Cells Voltage

In China's comprehensive strategy to address climate change and facilitate a green and low-carbon transformation, the 3060 target represents a pivotal strategic decision, signifying China's formal commitment to global carbon neutrality. In accordance with the 3060 objective, China will progressively establish a more comprehensive clean energy hydrogen production and distribution infrastructure, which will facilitate the attainment of the strategic objective of carbon peaking. Hydrogen production by water electrolysis has emerged as a prevalent approach to hydrogen production in recent years, and the stability and efficiency of the electrolytic cell voltage play a pivotal role in determining the overall production efficiency. The electrolytic cell voltage is influenced not only by design-related factors but also by a multitude of external factors.

Factors Affecting Electrolysis Cells Voltage

Membrane structure:

The resistance and ionic conductivity of a membrane are influenced by a number of factors, including the material, thickness, porosity and surface properties. High-quality membrane materials have low resistance, facilitating the reduction of cell voltage.

Current density:

As the current density rises, the electrolytic cell voltage of the hydrogen electrolyzer typically rises for a number of reasons, including ohmic resistance, polarisation resistance and heat generation.

Potassium hydroxide concentration:

The concentration of potassium hydroxide directly influence on the conductivity of the electrolyte, which in turn affects the cell voltage. In general, the concentration of potassium hydroxide is maintained at approximately 30%, whereas sodium hydroxide is typically used at a concentration of approximately 25%.

Spacing between two electrodes:

The spacing between the electrodes is considerable, the ion migration path is lengthy, and it is susceptible to the influence of the electrolyte resistance, which will result in an elevated voltage within the cell. An appropriate spacing can ensure the uniform distribution of the electric field; otherwise, it will have an adverse impact on the stability of the voltage and its value.

Lye circulation volume:

The circulation of lye serves to maintain the concentration of electrolyte in the vicinity of the electrode surface, thereby exerting an influence on the cell voltage. Furthermore, if the circulation volume is insufficient, the products will accumulate in the vicinity of the electrode surface, which will result in an impeded contact between the electrolyte and the electrode. This, in turn, will lead to an elevated cell voltage.

Temperature:

An increase in temperature reduces the viscosity of the electrolyte, accelerates the movement of ions, enhances the electrical conductivity, and diminishes the activation energy of the electrode reaction. These effects contribute to a reduction in the cell voltage. However, excessive temperatures may give rise to additional problems, necessitating the maintenance of a precise temperature range.

Impurities in lye:

The participation of lye impurities in the electrode reaction or their contamination of the plugging membrane can result in alterations to the reaction path and conductivity, which may subsequently lead to an increase in the voltage of the cell.

Electrode active coatings:

The electrode-active coatings, exemplified by specific precious metal catalysts, can enhance electrode activation and concomitantly diminish the requisite reaction voltage.

The number of starts and stops:

Each start-up and shutdown will produce a certain degree of polarization on the electrode surface. This polarization will gradually accumulate with the increase in the number of start-ups and shutdowns, resulting in an increasing over potential on the electrode surface. Furthermore, frequent start-up and shutdown may also affect the performance of the membrane.