John Xu is a research scientist in the lab of mechanical engineer Friedrich “Fritz” Prinz, where the two are known for their work on creating fuel cells for next-generation cars. When the novel coronavirus struck, they looked for ways their deep understanding of electrochemical processes might be useful against the pandemic. Their contribution is a new type of protective face mask that extracts and concentrates oxygen from the air to avoid the considerable side effects of oxygen deficiency that can accompany prolonged N95 mask use while preventing the spread of the virus.

Xu, who received his PhD in Mechanical Engineering in 2016, spoke to us about their work. Excerpts follow:

What problem did you set out to solve?

modified N95 face mask

Stanford research scientist John Xu demonstrating a modified N95 face mask that he and his colleagues developed. (Image credit: Andrew Brodhead)

We’ve all become familiar with the value of surgical face masks in both preventing infection or, in the case of an already infected person, in preventing further spread of the disease. The masks essentially filter the air coming in and out of the lungs, trapping the virus and other particles in its mesh. Through the COVID-19 crisis, many have become familiar with N95 masks, which filter out 95 percent or more of small particulate matter from the air – including the virus.

But in filtering those particles, N95 masks can also make it harder to breathe. Based on literature and confirmed by our measurements, N95 masks are estimated to reduce oxygen intake by anywhere from 5 percent to 20 percent. That’s significant, even for a healthy person. It can cause dizziness and lightheadedness. For healthy people, these side effects are temporary and usually not an issue. But if you are severely ill and are continuously wearing an N95 mask for several hours at a time, it can damage the lungs. For a patient in respiratory distress, it can even be life threatening.

*See editor’s note at the bottom.

How have you tried to address that problem?

The Prinz Laboratory team was already working on electrochemical conversion of oxygen from the air for energy applications for sustainable automobiles. It’s important to remember that ambient air is only about 21 percent oxygen, so we wanted to see if we could extract more oxygen to provide a more-concentrated flow – we call it oxygen enrichment. It’s a common process in combustion and electrochemical fuel conversion because you need oxygen to burn things. Our goal was to develop a portable device that uses these electrochemical processes to enrich oxygen from the ambient air.

We are working on a couple of ways to do this. The first is a classical process known as splitting water. If you collect water and run an electrical current through it, the additional electrons will cause the water to split into pure hydrogen and pure oxygen. The hydrogen can be used as a fuel and the oxygen goes to the mask to be breathed. The other reaction we’re working on involves moving oxygen-containing anions – a negatively charged atom or atoms – through a membrane to isolate the oxygen on one side where it can be collected and directed to the mask.

Do you have a working prototype?

We do. It is a small box that is worn at the waist with a tube that extends to the face mask.

The device we have created actually generates clean, pure oxygen using this electrochemical process to supplement loss of oxygen due to masking. We think it can protect the respiratory system of long-term mask wearers, particularly healthcare workers and patients.

Who is the primary target for this device?

We are targeting this to anyone who has to wear a mask for the long term, first responders, doctors, nurses and even patients who don’t want to infect others. In the near term, we hope to get these into healthcare workers as soon as possible. We are working with Allison Okamura and her postdoc Ming Luo to make it a wearable pneumatic device with additional engineering physics and user-experience design modifications.

Editor’s Note: The story was edited on 7/2/2020 to emphasize that the masks being discussed are N95 masks.

To read all stories about Stanford science, subscribe to the biweekly Stanford Science Digest.

Media Contacts

Tom Abate, Stanford Engineering: (650) 815-1602,