Ultrasmall VMnMoS_x Clusters with Bifunctional OER/HER Performance for Highly Efficient Water Splitting

Area of Science:

• Materials Science
• Electrochemistry
• Catalysis

Background:

• Electrochemical water splitting is crucial for green hydrogen production.
• Developing efficient anode (oxygen evolution reaction, OER) and cathode (hydrogen evolution reaction, HER) catalysts is essential.

Purpose of the Study:

• To synthesize and characterize ultrasmall S-doped VMnMo-based cluster catalysts (s-VMnMoSx) for enhanced bifunctional OER/HER activity.
• To investigate the effect of catalyst particle size on OER/HER performance.

Main Methods:

• Hydrothermal sulfidation of polyoxometalates to create S-doped VMnMo-based clusters (s-VMnMoSx).
• Electrochemical testing for OER and HER activity, including overpotentials and cell voltage for overall water splitting.
• Experimental and theoretical calculations to elucidate active sites and energy barriers.

Main Results:

• s-VMnMoSx catalyst demonstrated ultralow overpotentials for OER (290 mV) and HER (181 mV) at 500 mA cm⁻².
• Achieved a low cell voltage of 1.72 V for overall water splitting at 500 mA cm⁻² with negligible deactivation over 1000 hours.
• Large particle size catalysts (l-VMnMoSx) showed poor performance, indicating the critical role of ultrasmall cluster size.

Conclusions:

• Ultrasmall s-VMnMoSx catalysts exhibit superior bifunctional OER/HER performance compared to larger counterparts.
• Tuning catalyst size to the cluster regime alters active sites (V for OER, Mo for HER) and lowers energy barriers, leading to enhanced catalytic efficiency.
• This work highlights the potential of size-controlled S-doped VMnMo-based clusters for efficient green hydrogen production.