Isolation Strategy towards Earth-Abundant Single-Site Co-Catalysts for Photocatalytic Hydrogen Evolution Reaction

Abstract

Achieving efficient photocatalytic water splitting remains one of the most vital challenges in the photocatalysis field, as the performance of contemporary heterogeneous catalysts is still limited by their insufficient activity and low predictability. To address this challenge, this work takes inspiration from the concept of heterogeneous single-metal-site catalysts (HSMSCs) and follows the idea of site-isolation, aiming towards single-site co-catalyst species and a higher atom-utilization efficiency. We synthesized a set of photocatalysts through an adsorption-limited wet impregnation process using bare and phosphate-modified TiO2 as model supports and earth-abundant metals (Cu and Ni) with various loadings (0.008–5 wt.%) as co-catalyst species. The catalysts are characterized by TXRF for the determination of the real co-catalyst loadings, UV-vis and FTIR spectroscopes for semi-quantitative analysis of the metal state and binding modes to the substrate, and HRTEM for resolving the morphology of the sample’s surface. All samples were then evaluated towards the photocatalytic hydrogen evolution reaction (HER). We show that much higher turnover frequencies (TOFs) are obtained for both Cu- and Ni-based systems when lower co-catalyst loadings are used, which indicates an improved atom-utilization efficiency that reaches performances comparable to the noble Au co-catalyst. We also introduce a structural model to explain the observed TOF trends, which confirms that both earth-abundant systems undergo a strong structural reconstruction upon site-isolation towards smaller, perhaps even single-site-like species.

Effect of Co Doping on Electrocatalytic Performance of Co-NiS2/CoS2 Heterostructures

“…When the proportion of Co doping reaches 27%, the regular crystal basically disappears, and only irregular coral flowerlike structure can be seen on the carbon fiber. S2a and S3a, in order to analyze the activity difference between Co-NiS 2 /CoS 2 heterostructures and undoped NiS 2 , we measured different scanning rates (5,10,20,30,40,50,60,70,80, 90 and 100) by cyclic voltammetry (CV). As shown in Figures S2b and S3b, the electrochemical surface area (ECSA) of undoped and 27% doped Faraday double-layer capacitor (Cdl) is obtained.…”

“…Large scale use of pollution-free, green and sustainable energy is the future development trend [1][2][3]. Compared with traditional energy sources, the water produced by hydrogen combustion will not cause any pollution to the atmosphere and water resources [4][5][6][7]. At present, the common hydrogen production methods include photocatalysis and electrocatalysis, etc.…”

Electronegativity Assisted Synthesis of Magnetically Recyclable Ni/NiO/g-C3N4 for Significant Boosting H2 Evolution

“…Ni 2+ introduction decreases the intensity of N-H and N-H 2 groups on the surface of g-C 3 N 4 , likely due to the Ni loading on the cavity of the heptazine ring of g-C 3 N 4 ( Figure S2 ) [ 13 , 14 ], which shades the N-H stretching detected by IR. Furthermore, Ni 2+ introduction also decrease the intensity of the -OH pattern ( Figure 2 d), which indicates that the Ni 2+ species (as Lewis acid) also binds to the surface O - (as Lewis base) deriving from the dissociation of surface hydroxyl groups [ 15 ].…”

Main Hydrogen Production Processes: An Overview

“…In the case of palladium [93], a "series-parallel" reaction network has been proposed for describing the water splitting reaction using the mesoporous Pd-TiO2 and ethanol as organic scavenger (Figure 5) [94]. The addition of earth-abundant metals has a positive effect, in particular in the case of Ni [95] and Cu [96,97]. A high activity in hydrogen evolution under visible light has been demonstrated also for solid solutions of cadmium and manganese sulfides, due to their valence and conduction band position tuning, and for composite photocatalysts, CdS-β-Mn3O4-MnOOH, due to the ternary heterojunction formation [98].…”