# FeSe2-BiSe2-CoSe2 Ternary Heterojunction for Efficient Hydrogen Evolution Reaction Under pH-Universal

## TL;DR

A new ternary heterojunction material is developed for efficient hydrogen production in both acidic and alkaline conditions.

## Contribution

A novel FeSe2-BiSe2-CoSe2 heterojunction is synthesized with pH-universal hydrogen evolution reaction performance.

## Key findings

- The material shows 44 mV overpotential in acidic media and 188 mV in alkaline media.
- It has a Tafel slope of 108 mV dec−1 in acid and 45 mV dec−1 in base.
- The structure enables efficient electron diffusion and charge transfer for enhanced catalytic activity.

## Abstract

The construction of heterostructures has been recognized as an effective strategy for enhancing material activity and stability. Herein, a ternary heterojunction FeSe2-BiSe2-CoSe2 was synthesized via a hydrothermal selenidation reaction. The significant electronegativity difference between Bi and Fe/Co triggers charge transfer within the FeSe2-BiSe2-CoSe2 lattice. Furthermore, the abundant pore structure of FeSe2-BiSe2-CoSe2 provides efficient pathways for electron diffusion, significantly enhancing the HER catalytic kinetics. Results demonstrate that FeSe2-BiSe2-CoSe2 exhibits outstanding HER activity in both acidic and alkaline media. In 0.5 M H2SO4, it exhibits an overpotential of only 44 mV with a Tafel slope of 108 mV dec−1. In 1 M KOH, the corresponding overpotential is 188 mV, with a Tafel slope of 45 mV dec−1 at 10 mA cm−2. This study constructs electron-rich active sites through electronic structure regulation, providing valuable insights for designing low-cost, high-performance transition metal selenide HER catalysts.