Total Turnover Frequency Value Research Articles

Co, Ni-based nanoparticles supported on graphitic carbon nitride nanosheets as catalysts for hydrogen generation from the hydrolysis of ammonia borane under broad-spectrum light irradiation

From the viewpoint of tailoring the atomic and nanoscale structures of semiconductors to enhance the solar-to-hydrogen energy conversion, we employed an in-situ gas template-assisted co-polymerization route, where melamine and 2,4,6-triaminopyrimidine were co-monomers and NH4Cl was the in-situ gas template, to synthesize porous broad-spectrum light-responsive carbon nitride nanosheet (termed as CNN) species with increased π-electron availability. Then we developed CNN-supported Co and Ni nanoparticles (NPs) for catalytic hydrogen generation from aqueous ammonia borane (NH3BH3) under light irradiation (λ ≥ 420 nm) at room temperature. Though all the Co-based catalysts had the similar activities with total turnover frequency (TOF) values of 37.5–44.1 min−1 in the dark, they exhibited significantly different and enhanced photocatalytic activities. Remarkably, the optimized catalyst had a total TOF value of 123.2 min−1, exceeding the values of reported non-noble metal catalysts. Moreover, the porous CNN species possessed the C-substitution for N, tunable narrow bandgaps of 0.71–2.34 eV and efficient separation of photogenerated charge carriers. This resulted in the enriched electron density of metal NPs and the apparent quantum yield of 66.9% at 420 nm.

Non-noble trimetallic Cu-Ni-Co nanoparticles supported on metal-organic frameworks as highly efficient catalysts for hydrolysis of ammonia borane

Highly dispersed non-noble trimetallic Cu-Ni-Co nanoparticles can be successfully immobilized onto the pores of the metal-organic framework, MIL-101, by a simple solvent evaporation method. The Cu-Ni-Co@MIL-101 nanoparticles exhibit excellent catalytic effect on the hydrolysis of ammonia borane at 25 °C. Compared to their bimetallic and monometallic counterparts, Cu-Ni-Co trimetallic catalysts display superior catalytic activity. Careful investigation reveals that Cu0.8Ni0.1Co0.1@MIL-101 (Cu:Ni:Co atomic ratio = 8:1:1) displays a total turnover frequency (TOF) value of 72.1 molH2 molcat−1 min−1. This is the highest TOF value reported for non-noble metal catalysts to date and is even superior to values afforded by some noble metal catalysts (Au, Pt and Pd). The apparent activation energy of Cu0.8Ni0.1Co0.1@MIL-101 can be as low as 29.1 kJ mol−1. This remarkable enhancement in catalytic performance is attributed to the large catalyst surface as well as the synergetic effect between Cu, Ni, and Co supported on MIL-101. This study provides a new strategy for the preparation of high performance non-noble metal catalysts for the practical hydrolysis of hydrogen storage systems, thereby fast-tracking the application of ammonia borane in fuel cells.

Synergistic catalysis of MCM-41 immobilized Cu–Ni nanoparticles in hydrolytic dehydrogeneration of ammonia borane

Bimetallic Cu–Ni nanoparticles (NPs) were successfully immobilized in MCM-41 using a simple liquid impregnation-reduction method. All the resulting composites Cu–Ni/MCM-41 catalysts with various contents of Cu–Ni, and in particular Cu0.2Ni0.8/MCM-41 sample, outperform the activity of monometallic Cu and Ni counterparts and pure bimetallic Cu0.2Ni0.8 NPs in hydrolytic dehydrogeneration of ammonia borane (AB) at room temperature. The Cu0.2Ni0.8/MCM-41 catalyst exhibits excellent catalytic activity with a total turnover frequency (TOF) value of 10.7 mol H2 mol catalyst−1 min−1 and a low activation energy value of 38 kJ mol−1 at room temperature. In addition, Cu0.2Co0.8/MCM-41 also exhibits excellent activity with a TOF value as high as 15.0 mol H2 mol catalyst−1 min−1. This obtained activity represents the highest catalytic active of Cu-based monometallic and bimetallic catalysts up to now toward the hydrolytic dehydrogeneration of ammonia borane (AB). The unprecedented excellent activity has been successfully achieved thanks to the strong bimetallic synergistic effects among the Cu–Ni (or Co) NPs of the composites.