Ligand-Centered Hydrogen Evolution with Ni(II) and Pd(II)DMTH

Area of Science:

• Inorganic Chemistry
• Electrocatalysis
• Renewable Energy

Background:

• The hydrogen evolution reaction (HER) is crucial for producing clean hydrogen fuel.
• Developing efficient and robust electrocatalysts is key to advancing HER technologies.
• Noninnocent ligands offer unique electronic properties for catalytic applications.

Purpose of the Study:

• To synthesize and characterize novel nickel (Ni) and palladium (Pd) complexes for HER.
• To investigate the catalytic mechanism and efficiency of these complexes.
• To explore the role of ligand protonation in the electrocatalytic process.

Main Methods:

• Synthesis and characterization of NiL¹ and PdL¹ complexes using spectroscopic and electrochemical techniques.
• Spectrophotometric titration to determine the pKa of the hydrazino nitrogen.
• Cyclic voltammetry to study redox properties and HER activity in acetonitrile.
• Kinetic isotope effect (KIE) studies and Density Functional Theory (DFT) computations to elucidate the reaction mechanism.

Main Results:

• NiL¹ and PdL¹ complexes were successfully synthesized and characterized.
• The basic hydrazino nitrogen exhibited pKa values of 12.71 (NiL¹) and 13.03 (PdL¹).
• High turnover frequencies were achieved: 6150 s^-1 for NiL¹ at 0.74 V and 8280 s^-1 for PdL¹ at 0.44 V.
• KIE studies and DFT calculations indicated a ligand-centered HER mechanism involving proton-coupled electron transfer.

Conclusions:

• The synthesized NiL¹ and PdL¹ complexes are highly effective electrocatalysts for the hydrogen evolution reaction.
• The HER mechanism involves proton-coupled electron transfer, with the metal centers remaining in the +2 oxidation state.
• These findings highlight the potential of noninnocent ligand-based complexes for efficient hydrogen production.