Setting Electrons Free: The Catalyst That Broke a Decades-Old Redox Rule

Every redox reaction is a story about who gets the electrons. For decades chemists have worked with a simple rule: if two molecules are competing for an electron, the one that is easier to reduce wins. In August 2026 a team from the University of Wisconsin–Madison, Colorado State University and the University of Colorado Boulder reported in Nature a catalyst that gets around that rule^[1]. The idea is surprisingly simple: set the electron free first, and choose the winner afterwards.

Redox in one paragraph

Reduction is gain of electrons; oxidation is loss (OIL RIG). A reducing agent gives electrons away; an oxidising agent accepts them. Some substances accept electrons much more readily than others. At A-Level you measure that with standard electrode potentials (E°): the more positive the E°, the more easily a species is reduced. For example, Cu²⁺ (E° = +0.34 V) is reduced far more easily than Zn²⁺ (E° = −0.76 V), which is why zinc metal displaces copper from copper sulfate solution, but copper cannot displace zinc.

The rule, and why it is a problem

In organic synthesis, chemists often want to add an electron to a particular molecule to make it react. The trouble comes when a mixture contains two molecules (or two parts of one molecule) that could accept it. Normally the electron goes to whichever is easier to reduce^[1]. If the one you actually want to react is the harder one, you are stuck: the electron is always captured by the other.

The trick: release the electron first

Over five years, Zachary Wickens's group developed a new family of photoredox catalysts, molecules that use light energy to drive electron transfer^[1]. When lit, this catalyst does not hand its electron straight to a neighbouring molecule. Instead it releases it directly into the surrounding solution, creating an extremely reactive free (solvated) electron^[1]. As the team put it, “anything is better than the electron freely floating in solution”^[1]: the free electron reduces whatever it meets, easy or hard.

The selectivity then comes after the transfer. The molecule you want goes on to react and form product, which removes it from the competition. An unwanted molecule that received the electron has nowhere useful to go, so it passes the electron back and is recycled^[1]. Over time, the product builds up from the “harder” molecule even though the “easier” one is present. Computational studies (Robert Paton, Colorado State) and spectroscopy (Niels Damrauer, CU Boulder) helped confirm the mechanism^[1].

“This is not just another synthetic method; it's a new way to design redox reactions.” Zachary Wickens^[1]

Why it could matter

• Medicines: drug molecules often contain several groups that could be reduced; being able to choose the harder one opens new routes^[1].
• Materials: new ways to build and modify polymers and functional molecules^[1].
• Light-driven chemistry: another example of using light instead of harsh reagents or high temperatures.

The work is at the laboratory stage, and how widely it applies is still being explored.

This is a nice example to quote in a redox or electrochemistry answer, and it shows that even well-known rules have clever exceptions. Our chemistry tutoring covers electrode potentials step by step, and our post on how catalysts work explains reaction pathways and activation energy.