# Crystalline Ni3S2 Nanorods Tuned by Low-Crystalline NiCoSx with Built-In Electric Field for Efficient Overall Water Splitting

## TL;DR

A new electrocatalyst made of Ni3S2 nanorods and NiCoSx shell improves water splitting efficiency and stability.

## Contribution

A novel interface engineering strategy creates a stable and efficient water-splitting electrocatalyst with a built-in electric field.

## Key findings

- The NiCoSx@Ni3S2 heterostructure achieves low HER/OER overpotentials of 346/520 mV@1000 mA cm−2.
- The material shows an ultralow cell voltage of 2.10 V@1000 mA cm−2 for overall water splitting.
- The catalyst maintains stability for up to 400 hours of operation.

## Abstract

Low-crystalline NiCoSx-armored Ni3S2 nanorod heterostructure inhibits sulfide loss.Built-in electric field effect induced by work function accelerates electron transfer.The NiCoSx@Ni3S2/NF exhibits superior hydrogen and oxygen evolution reactions activity and stability.

Low-crystalline NiCoSx-armored Ni3S2 nanorod heterostructure inhibits sulfide loss.

Built-in electric field effect induced by work function accelerates electron transfer.

The NiCoSx@Ni3S2/NF exhibits superior hydrogen and oxygen evolution reactions activity and stability.

The online version contains supplementary material available at 10.1007/s40820-026-02151-6.

Efficient overall water splitting (OWS) technology has been highly demanded across the world, of which the key is the development of active and stable electrocatalysts for both hydrogen and oxygen evolution reactions (HER/OER). Herein, novel crystalline Ni3S2 nanorods tuned by low-crystalline NiCoSx (NiCoSx@Ni3S2) are synthesized via an ion-exchange strategy. The built-in electric field at the heterogeneous interface driven by work function difference, facilitates rapid electron transfer from Ni3S2 to NiCoSx via a robust Ni–S–Co bond bridge. This synergistic combination of the conductive crystalline core and low-crystalline shell optimizes the d-band center, balancing intermediate adsorption/desorption, speeding up water dissociation, enhancing hydrogen adsorption/desorption for HER, and lowering the energy barrier for OER, ultimately boosting OWS efficiency. The defect-rich, low-crystalline NiCoSx shell, bonded to the crystalline core via Ni–S–Co bonds, serves as a protective armor, enabling dynamic reconstruction into NiCoOOH and suppresses sulfide leaching, ensuring catalytic stability. The optimized NiCoSx@Ni3S2 achieves low HER/OER overpotentials of 346/520 mV@1000 mA cm−2, evidenced by an ultralow cell voltage of 2.10 V@1000 mA cm−2 for OWS and long-term durability up to 400 h. The work paves a novel way to fabricate sulfur-based electrocatalysts with high yet balanced activity and stability for OWS via an interface engineering strategy.

The online version contains supplementary material available at 10.1007/s40820-026-02151-6.