Harnessing Redox Flow Batteries for Clean Energy and Desalination

Two of the greatest challenges humanity faces in an era of climate emergency and transition to renewable energies are obtaining drinking water and energy storage. One of the most common and efficient solutions for the first challenge is reverse osmosis desalination, and for the second, batteries. However, in laboratories, scientists and engineers are already exploring new technologies that could combine both solutions to advance the energy transition. We're talking about desalinating redox flow batteries or Redox Flow Desalination (RFD) technology, a field in which New York University has recently made considerable advances. In this article, you will learn about:

• What redox flow batteries are
• The leap to desalinating redox flow batteries
• New York University's solution

What are redox flow batteries?

Before explaining what a desalinating redox flow battery is, it’s important to understand the general concept of redox batteries. This technology works by storing energy in liquid solutions called electrolytes, which contain chemical compounds capable of changing from an oxidized state to a reduced state and vice versa.

During operation, two different types of electrolytes are pumped from separate tanks through a central electrochemical cell. In this cell, the electrolytes interact through an ion-exchange membrane that allows the passage of ions but separates the two liquids. The chemical reaction that occurs in this cell generates electricity, which can be used or stored as needed.

These batteries have a long lifespan, as they can withstand many charge and discharge cycles without significant degradation. They are particularly useful for storing renewable energy, such as solar or wind power, as they can store excess energy generated and release it when production is low.

The new generation of desalinating redox batterie

Redox Flow Desalination (RFD) is an innovative technique that combines water desalination and energy storage into a single system. In this case, it operates by circulating salt solutions and redox agents through electrochemical cells. Ion-exchange membranes separate these solutions, allowing the selective transfer of ions, resulting in the extraction of salt from seawater and the production of fresh water.

The RFD process not only produces drinking water but also allows for the storage of excess energy from renewable sources. During desalination, the system can store energy in the redox molecules and then release it when needed, acting as a battery. This energy storage and release capability is crucial for balancing the fluctuation in renewable energy demand and water needs.

Advances at New York University

Both redox flow batteries and desalination systems based on this technology are far from widespread implementation. The former suffers from certain disadvantages, such as the need for large storage tanks due to their low energy density, while the latter are still in the experimental phase. However, New York University has managed to improve redox flow desalination through a new approach that increases desalination efficiency by 20%.

The RFD system they developed uses a structure of four channels separated by ion-exchange membranes (IEM). Research highlights that increasing the flow rate in the electrolyte channels reduces resistance at the electrolyte-membrane interface. This significantly improves salt removal and the system's energy efficiency. For example, increasing the flow rate from 5 to 50 mL/min boosts the salt removal rate by 16.7 times while reducing energy consumption.

Currently, the most common technology for storing renewable energy is lithium batteries, but who knows if redox flow batteries are destined to play a significant role in the decarbonization of the economy and, in parallel, help alleviate drinking water needs.

Sources:

• New York University