Habib Baydoun

Efficient Water Oxidation Using CoMnP Nanoparticles.

The development of efficient water oxidation catalysts based on inexpensive and Earth-abundant materials is a prerequisite to enabling water splitting as a feasible source of alternative energy. In this work, we report the synthesis of ternary cobalt manganese phosphide nanoparticles from the solution-phase reaction of manganese and cobalt carbonyl complexes with trioctylphosphine. The CoMnP nanoparticles (ca. 5 nm in diameter) are nearly monodisperse and homogeneous in nature. These CoMnP nanoparticles are capable of catalyzing water oxidation at an overpotential of 0.33 V with a 96% Faradaic efficiency when deposited as an ink with carbon black and Nafion. A slight decrease in activity is observed after 500 cycles, which is ascribed to the etching of P into solution, as well as the oxidation of the surface of the nanoparticles. Manganese-based ternary phosphides represent a promising new system to explore for water oxidation catalysis.

Ligand Transformations and Efficient Proton/Water Reduction with Cobalt Catalysts Based on Pentadentate Pyridine‐Rich Environments

A series of cobalt complexes with pentadentate pyridine-rich ligands is studied. An initial Co(II) amine complex 1 is prone to aerial oxidation yielding a Co(III) imine complex 2 that is further converted into an amide complex 4 in presence of adventitious water. Introduction of an N-methyl protecting group to the ligand inhibits this oxidation and gives rise to the Co(II) species 5. Both the Co(III) 4 and Co(II) 5 show electrocatalytic H2 generation in weakly acidic media as well as in water. Mechanisms of catalysis seem to involve the protonation of a Co(II)-H species generated in situ.

The Mechanisms of Rectification in Au|Molecule|Au Devices Based on Langmuir–Blodgett Monolayers of Iron(III) and Copper(II) Surfactants†

Langmuir-Blodgett films of metallosurfactants were used in Au|molecule|Au devices to investigate the mechanisms of current rectification.

Synthesis and oxygen evolution reaction (OER) catalytic performance of Ni2−xRuxP nanocrystals: enhancing activity by dilution of the noble metal

Aiming to create an efficient, less-expensive catalyst for the oxygen evolution reaction (OER), a synthetic protocol is developed to prepare ternary metal phosphide nanoparticles, Ni2−xRuxP, incorporating Ru, a traditional catalyst for OER, and Ni, a highly active but inexpensive metal. Using solution-phase arrested-precipitation reactions, crystalline Ni2−xRuxP particles could be realized for compositions up to x ≤ 1, whereas more Ru-rich compositions, including Ru2P, were amorphous. For x ≤ 1, particles are spherical, of sizes that vary between 5 and 10 nm in diameter (with a clear decreasing trend as the Ru amount is increased), and samples exhibit narrow size distributions (polydispersity < 15%). In contrast, amorphous Ru-rich phases exhibit worm-like morphologies. ICP-MS data indicate the actual metal ratio closely follows the target ratio employed in the synthesis. OER electrocatalytic activity was evaluated for selected compositions over the entire synthesis range (0 ≤ x ≤ 2). Intriguingly, Ru2P proved to be the least active phase (overpotential of 0.56 V at 10 mA cm−2 in 1.0 M KOH) with the best performance observed for the bimetallic Ni1.25Ru0.75P phase (overpotential of 0.34 V). The augmented activity at x = 0.75 is attributed, at least in part, to electronic activation of Ni by Ru, facilitating Ni oxidation and thus decreasing the kinetic barrier for OER.

Deactivation of a Cobalt Catalyst for Water Reduction through Valence Tautomerism

The activity of the water reduction catalyst [CoIII (L1 )(pyr)2 ]PF6 (1), where (L1 )2- is a bis-amido pyridine ligand and pyr is pyrrolidine, is investigated. Catalyst 1 has an overpotential of 0.54 V and a high observed TOF of 23 min-1 , albeit for a relatively short time. Considering the significant activity of 1 and aiming to improve catalyst design, a detailed structural and electronic study is performed to understand the mechanisms of deactivation. Experimental and theoretical evidence support that the metal-reduced [CoI (L1 )]- is in tautomeric equilibrium with the ligand-reduced [CoII (L1. )]- species. While [CoI (L1 )]- favors formation of a CoIII -H- relevant for catalysis, the [CoII (L1. )]- species leads to ligand protonation, structural distortions, and, ultimatley, catalyst deactivation.