Hydrogen on Cobalt Phosphide

Abstract

Cobalt phosphide (CoP) is one of the most promising earthabundant replacements for noble metal catalysts for the hydrogen evolution reaction (HER). Critical to HER is the binding of H atoms. While theoretical studies have computed preferred sites and energetics of hydrogen bound to transition metal phosphide surfaces, direct experimental studies are scarce. Herein, we describe measurements of stoichiometry and thermochemistry for hydrogen bound to CoP. We studied both mesoscale CoP particles, exhibiting phosphide surfaces after an acidic pretreatment, and colloidal CoP nanoparticles. Treatment with H 2 introduced large amounts of reactive hydrogen to CoP, ca. 0.2 H per CoP unit, and on the order of one H per Co or P surface atom. This was quantified using alkyne hydrogenation and Hatom transfer reactions with phenoxy radicals. Reactive H atoms were even present on the as-prepared materials. On the basis of the reactivity of CoP with various molecular hydrogen donating and accepting reagents, the distribution of binding free energies for H atoms on CoP was estimated to be roughly 51−66 kcal mol −1 (ΔG°H ≅ 0 to −0.7 eV vs H 2 ). Operando X-ray absorption spectroscopy gave preliminary indications about the structure of hydrogenated CoP, showing a slight lattice expansion and no significant change of the effective nuclear charge of Co under H 2flow. These results provide a new picture of catalytically active CoP, with a substantial amount of reactive H atoms. This is likely of fundamental relevance for its catalytic and electrocatalytic properties. Additionally, the approach developed here provides a roadmap to examine hydrogen on other materials.

Solvent-Free Mechanochemical Synthesis of Ultrasmall Nickel Phosphide Nanoparticles and Their Application as a Catalyst for the Hydrogen Evolution Reaction (HER)

“…Similar ligand exchanges have been shown to improve the hydrogen generation capabilities of both Au 71 and CoP nanocatalysts. 72 Therefore, an intimate interface between g-C3N4 and Ni2P NPs was formed that induced an effective electron transfer (Figure 5a). CN-NiP-Ex-300 and CN-NiP-Im-300 showed enhanced H2 evolution rates of 177.1 µmol g -1 h -1 and 233.9 µmol g -1 h -1 , respectively, which are much higher than that of samples obtained without prior ligand exchange (CN-NiP series) (Figure 6a).…”

In Situ Formation of a Sub-Nanometer Iridium Phosphide Catalyst from Supported Organometallic Species

“…While cobalt phosphide 7,17,18,21,22 and rhodium phosphide [23][24][25][26][27][28][29] catalysts have both been the subject of active study in recent literature, the catalytic properties [30][31][32][33] of iridium phosphides have been less explored outside of structural and physical studies over the last half century, [34][35][36][37][38][39][40][41][42][43][44][45] in part due to their difficult syntheses. 46 This is in spite of the fact that, given the similarity often observed in the behavior of metal phosphides to their metal analogues, iridium-derived catalysts have often been found to be exceptional catalysts for reactions of great industrial value 47, 48 such as alkane dehydrogenation.…”

“…1, 4, 5 Nanostructured nickel phosphide (Ni 2 P), for instance, has been shown to exhibit Ptlike effectiveness for HER, 6 and more recently, cobalt phosphide (CoP) has been explored as an efficient earthabundant alternative catalyst for the same process. 7 While the majority of catalysis involving these species has primarily focused on these reactions, fledgling efforts have also begun to appear looking at the application of metal phosphides for other reactions such as methane dry reforming 8 and NO dissociation/removal. 9 Such materials are yet relatively unexplored and their study continues to reveal new and interesting applications in catalysis.…”

Ethane dehydrogenation performance and high temperature stability of silica supported cobalt phosphide nanoparticles

“…P-Containing catalysts, also known as metal phosphides, are known particularly for hydrodesulfurization, hydrodeoxygenation, and hydrogenation reactions. [8][9][10][11][12][13] Additionally, many metal phosphides are made from earth abundant metals, such as Ni, Co, Mo, and Fe, and have been identified as promising alternatives to noble metal based catalysts for many industrially relevant reactions. 14,15 For light alkane dehydrogenation reactions, P promotion of Ni results in improved selectivity to the desired alkene as well as improved stability over monometallic Ni nanoparticles.…”