# Fast Thermoelectric Responses from Unconventional Na‐I Stoichiometry in Reduced Graphene Oxide Films

## TL;DR

This paper reports a new 2D thermoelectric material made from reduced graphene oxide with unconventional sodium-iodine ratios, showing fast responses to temperature changes.

## Contribution

The study introduces a novel Na-I@rGO film with fast thermoelectric responses due to a unique heterogeneous structure.

## Key findings

- Na-I@rGO film shows a peak thermoelectric current of ~650 nA at a ΔT of 40 K.
- The material has a Seebeck coefficient of ≈22.7 µV K−1 for ΔT between 2−40 K.
- The film responds to temperature changes in 0.6 seconds, suitable for detecting rapid temperature variations.

## Abstract

Thermoelectric materials composed of 2D structures have received extensive attention and research due to their potential properties. The development of novel 2D materials will provide many valuable technological characteristics for thermoelectric applications. Here, fast thermoelectric responses are reported from unconventional Na‐I stoichiometry in reduced graphene oxide films (Na‐I@rGO). The thermoelectric mechanism is based on the Seebeck effect caused by the heterogeneous structure between the rGO layers from Na2I and NaI. The formation of this heterogeneous structure is attributed to the gravity‐driven ion permeation during the preparation process and cation‐π interactions. Na‐I@rGO film exhibits a significant thermoelectric current at a temperature difference (ΔT) of 40 K (peak current ∼650 nA). The Seebeck coefficient of Na‐I@rGO film is ≈22.7 µV K−1 for a ΔT range of 2−40 K. Importantly, Na‐I@rGO film has a fast response (0.6 s) as a self‐powered sensing device, which is comparable to that of most other reported classical thermoelectric materials. The Na‐I@rGO sensor can be suitable for fast detecting transient extreme temperature variations, such as flame and liquid nitrogen. These findings can provide inspiration for the design of 2D thermoelectric structures on graphene films.

By coating the graphene oxide suspension and the dilute NaI solution layer‐by‐layer from bottom up, this work achieves a heterogeneous structure from asymmetry of the up and bottom surface Na and I atomic ratios in reduced graphene oxide (rGO) films, which exhibits fast thermoelectric responses.