Thermal Regenerating Ammonia Batteries

Calvin Chandler II
November 3, 2015

Submitted as coursework for PH240, Stanford University, Fall 2015


Fig. 1: The chemical process. (Source: C. Chandler II)

With the uncertain future of fossil fuels as a result of limited resources and global warming, it is essential to find alternative ways to harness energy. Currently many energy techniques such as solar, wind and hydroelectricity are being explored. However these methods are still inefficient. The problem with transferring these forms of energy into usable, electric batteries is that a large percentage of energy is lost as heat.

However what if there were batteries that harnessed this lost heat and restored the energy back into the batteries itself? As of now researches have found a way to create regenerating batteries that capture low-grade waste heat through the use of ammonia. These batteries have been tested to produce up to 60 watts of energy per square meter. [1]

What is TRAB?

TRAB stands for thermal regenerating ammonia batteries. These batteries consist of two copper electrode chambers with liquid ammonia added to the electrolyte surrounding the positively charged anode. This reaction will run until the copper electrons in the negatively charged cathode are spent. However, the battery captures thermal energy from an outside source to vaporize the ammonia and condense it back into a recharged liquid state. This positively recharged ammonia is deposited back into the original cathode chamber. Therefore the ammonia switches between the two chambers while conserving all parts of the original reaction. This creates a regenerative way of chemically producing energy by using heat as the driving force. The picture below serves as a visual reference to the chemical process in these batteries.

The Problematic Future of TRAB: Entropy

While in theory TRAB seems to be the answer to our energy crisis, in reality it fails to be a promising solution. The Second Law of Thermodynamics states that as energy is transformed it goes from an ordered state to a more disordered state. This irreversible process known as entropy never decreases in the universe, therefore the net entropy is always positive. The formula for entropy is given as follows, Δ S = Δ Q / T. In other words the change in entropy (J/K) is equal to the change in heat (J) divided by the temperature (K). These batteries operate at 345 K and absorb 236 J per second. [1] Based on calculations the entropy of the system is then 0.68 J/K. It is apparent then that these batteries do not harness an adequate amount of energy. This makes this technology very difficult to implement on a large scale when considering how much work and effort goes into making the batteries. In fact only 13% of outside thermal energy is ever stored electrically in these batteries due to this entropy conundrum. [1] Therefore these batteries still prove to be an inefficient solution to our energy crisis.

© Calvin Chandler. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.


[1] F. Zhang et al., "A Thermally Regenerative Ammonia-Based Battery for Efficient Harvesting of Low-Grade Thermal Energy as Electrical Power,'' Energy Env. Sci. 8, 343 (2015).