Hydrogen is an attractive alternative to fossil fuels for net reduction of carbon emissions. Electrolysis of water provides a clean and green process to produce hydrogen. The most efficient electrocatalyst for water splitting is platinum with an overpotential near zero volts, but its scarcity and high cost limits its use in the hydrogen evolution reaction (HER). This has stimulated development of new electrocatalysts for HER based-on earth abundant metals with low overpotentials. This study explores the HER activity of several Ni complexes containing modified versions of the diacetyl-bis(4-methyl-3-thiosemicarbazone) (ATSM) ligand. The Ni complexes shown in Fig. are coordinated to bis-thiosemicarbazone (1,4), thiosemicarbazone/alkylthiocarbamate (hybrid) (2,5) and bis-alkylthiosemicarbamate (3,6) ligands. The ligands are further related by systematic changes in the backbone groups from Me,Me to Me,Ph. Inks of the Ni complexes were prepared by sonicationg the mixture of complex, solvent and nafion. Thin films of the complexes were generated on GCE by drop casting followed by evaporation of the ink solvent. The HER activity of each catalyst modified GCE was evaluated using linear sweep voltammetry in 0.5 M H2SO4 solutions. Each electrode was evaluated during a series of reductive cycling steps. The overpotential for each modified electrode was determined using a current density of -10 mA/cm2. Based on the overpotentials and impedance measurements at peak reductive cycling, complex 2 showed the catalytic activity (η = 400 mV) similar to 1 (η = 393 mV). Charge transfer resistance for 2 was found to be 80 Ω, while for 1 it was 146 Ω, which didn’t change over the course of 1000 reductive cycling. In addition, this complex showed only a small increase in overpotential after 1000 reductive cycling and the modified surface was found to be very stable. Complexes 4 and 5 showed similar overpotentials of 525 mV, whereas complexes 3 and 6 showed slightly higher overpotentials (650 mV and 700 mV), respectively, and very high charge transfer resistance. This study demonstrates HER activity of structurally similar molecular catalysts can be tuned by slight modifications of the ligand framework.

Evaluating the effect of ligand modification on HER activity of a series structurally related N2S2 nickel (II) electrocatalysts

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.