Hydrogen evolution problem in flow batteries

Do aqueous flow batteries produce hydrogen?

As with some other aqueous flow batteries, they can experience significant rates of hydrogen generation (ca. 1–10% of the nominal operating current density). This hydrogen evolution represents a loss of protons from the electrolyte and it also leads to a chemical imbalance with each charge-discharge cycle.

Do hydrogen side-reactions cause electrolyte imbalance in all-iron flow batteries?

Conclusions Hydrogen side-reactions lead to an electrolyte imbalance in all-iron flow batteries, and this occurs simultaneously for iron and hydrogen species. Fortunately, this problem can be corrected using an appropriate rebalancing system.

What are the principles of sealed iron flow batteries?

Abstract Principles of sealed iron flow batteries are introduced and a semi-empirical model that incorporates the hydrogen evolution reaction and electrolyte rebalancing is developed. Hydrogen generation rates are measured using pressure measurements in sealed vessels.

Why do all-iron batteries generate more hydrogen during charging?

For the all-iron battery under the conditions tested, the rate of hydrogen generation during charging was two to five times larger than during discharging; this effect can likely be attributed to the more negative potential of the electrode during charging compared to the more positive potential during discharging.

What happens when a hybrid battery is charged?

Table I.  All-iron hybrid battery reactions. When the battery is charged, ferrous ions (Fe2 +) are reduced to iron metal at the negative electrode and oxidized to ferric ions (Fe3 +) at the positive electrode. Electrode Reaction Equation Negative Positive Cell

Why is a fuel cell important in a flow battery system?

The fuel cell facilitated the spontaneous reaction between hydrogen and ferric (Fe3 +) ions, given by Equation 4, and was considered to be one of the most important features of the flow battery system.15Equation 4, the hydrogen-ferric ion recombination reaction, has a standard cell potential of 770 mV.