Electrocatalytic Hydrogen Evolution under Acidic Aqueous Conditions and Mechanistic Studies of a Highly Stable Molecular Catalyst

Abstract

Electrocatalytic activity of a water-soluble nickel complex, [Ni(DHMPE)] (DHMPE = 2-bis(di(hydroxymethyl)phosphino)ethane), for the hydrogen evolution reaction (HER) at pH 1 is reported. The catalyst functions at a rate of ∼10 s (k) with high Faradaic efficiency. Quantification of the complex before and after 18+ hours of electrolysis reveals negligible decomposition under catalytic conditions. Although highly acidic conditions are common in electrolytic cells, this is a rare example of a homogeneous catalyst for HER that functions with high stability at low pH. The stability of the compound and proposed catalytic intermediates enabled detailed mechanistic studies. The thermodynamic parameters governing electron and proton transfer were used to determine the appropriate reductants and acids to access the catalytic cycle in a stepwise fashion, permitting direct spectroscopic identification of intermediates. These studies support a mechanism for proton reduction that proceeds through two-electron reduction of the nickel(II) complex, protonation to generate [HNi(DHMPE)], and further protonation to initiate hydrogen bond formation.

Directing the reactivity of metal hydrides for selective CO 2 reduction

“…Understanding the reactivity of metal hydrides is key to controlling the bifurcating reaction pathways that ultimately determine selectivity. Most selective catalysts for CO 2 reduction utilize kinetic inhibition (or a high-transition state barrier) to minimize H 2 evolution.In this report, we utilize a thermodynamic approach to describe the reactivity of metal hydrides with H + and CO 2 by applying known free energy relationships (14,(17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28). We depict our findings in a diagram (Fig.…”

“…Eq. 4 has successfully been applied to identify and optimize electrocatalysts for H 2 evolution (26,(31)(32)(33)(34)(35)(36)(37)(38) and H 2 oxidation (31)(32)(33)(34)(39)(40)(41)(42), and to achieve reversible reactivity (43,44).The relationship between pK a , hydricity, and H 2 evolution in acetonitrile is quantitatively depicted in Fig. 2A.…”

Homolytic versus Heterolytic Hydrogen Evolution Reaction Steered by a Steric Effect

“…The viability of a hydrogen‐based energy society is depended on efficient and durable production of hydrogen . Recent efforts have resulted in the identification of many molecular catalysts for hydrogen evolution . Despite these achievements, however, understanding and further controlling reaction processes are still highly challenging .…”

Convenient Immobilization of Cobalt Corroles on Carbon Nanotubes through Covalent Bonds for Electrocatalytic Hydrogen and Oxygen Evolution Reactions

“…[1][2][3] During the last decade,avariety of molecular complexes based on earth-abundant transition-metal elements including Mn, [4][5][6][7] Fe, [8][9][10][11][12][13][14] Co, [15][16][17][18][19][20][21] Ni, [22][23][24][25][26][27][28] and Cu [29][30][31][32][33] have been identified as catalystsf or these two reactions. [1][2][3] During the last decade,avariety of molecular complexes based on earth-abundant transition-metal elements including Mn, [4][5][6][7] Fe, [8][9][10][11][12][13][14] Co, [15][16][17...…”

“…This is likely because the large surface area and good electricalc onductivity of CNTsc an be well preserved during the amidationr eactionu nder mild conditions.The development of inexpensive, efficient, and robust electrocatalysts for the hydrogen evolutionr eaction (HER) and the oxygen evolution reaction( OER) has attracted increasing interest because of their appealing applicationsi nn ew energy technologies. [1][2][3] During the last decade,avariety of molecular complexes based on earth-abundant transition-metal elements including Mn, [4][5][6][7] Fe, [8][9][10][11][12][13][14] Co, [15][16][17][18][19][20][21] Ni, [22][23][24][25][26][27][28] and Cu [29][30][31][32][33] have been identified as catalystsf or these two reactions. To make these well-designed molecular catalysts useful in practice, they need to be immobilizedo ne lectrode materials.…”