Can NFC transfer power as well as data?
Transferring power is the first thing NFC does, before any data moves: a passive tag runs entirely on energy taken from the reader. The amount is minute, enough for a chip and nothing more. NFC is not a charging technology, and treating it as one leads to disappointment.
It already does, constantly
Every read is a power transfer. The tag has no battery, so before a single bit moves, the reader has to deliver enough energy to boot a chip. Data comes second and only exists because power came first.
So the question is not whether NFC can transfer power. It is how much.
The scale of what crosses the gap
Enough to run a chip that stores a few hundred bytes and answers a reader. That is microwatts, delivered over a coupling that collapses within centimetres.
Put next to anything people call charging, the gap is not incremental. A phone battery holds enough energy that supplying it through an NFC coupling would take an implausibly long time, and the coupling would need the two devices held motionless throughout.
Where wireless charging differs
Qi charging pads use the same underlying principle, induction between two coils, and almost nothing else in common. They run at a much lower frequency, use larger coils designed to sit nearly touching and aligned, and are built to move watts rather than microwatts.
The NFC Forum has also specified a wireless charging profile that reuses the 13.56 MHz link for small amounts of power, aimed at things like styluses and earbuds rather than phones. The NFC Forum publishes it as the Wireless Charging specification, whose negotiated mode defines four power classes of 250, 500, 750 and 1000 milliwatts.
The two systems fight each other
A tag sitting on a wireless charging pad, or stuck to the back of a phone over its charging coil, will very often stop being readable. Two coils competing for the same space detune each other, and the failure is usually complete rather than partial.
The one case that genuinely benefits
Battery free sensors are where power transfer stops being a curiosity. A tag with a temperature or moisture sensor built in draws its energy from the reader at the moment of measurement, reports a value, and returns to being inert.
The trade is severe and worth stating plainly: such a tag cannot log anything between reads, because it is not running between reads. It answers what conditions are like now, at the instant you tap it. If you need a history, you need a battery, and then you no longer have a passive tag.
Frequently asked questions
Can I charge my phone with NFC?
No. The energy that crosses an NFC coupling is measured in microwatts, and a phone battery needs several watts to charge in any reasonable time. Nothing about the technology can be tuned to bridge that difference.
Can NFC power a small LED?
Some tags include a driver capable of lighting a small indicator while inside a reader's field, which is used for visual confirmation on certain products. It lights only while the phone is held there, and goes out the instant you move away.
Why does my tag stop working near a charging pad?
The charging coil and the tag antenna occupy the same space and detune each other. Move the tag a few centimetres away from the coil, or use a tag designed for use on metal, which includes a ferrite layer that isolates it.
Do battery assisted tags exist?
Yes, and they are a different category. Adding a battery allows logging between reads and longer range, and it also adds cost, thickness, a service life and disposal constraints. Most deployments that consider one end up not needing it.