Carbon-coated nickel phosphide enhances efficiently electron transfer of cadmium sulfide for photocatalytic hydrogen production.

The capacitance of a co-catalyst can be likened to a "double-edged sword". Α co-catalysts with high capacitance can store photoexcited electrons, thereby facilitating charge separation within the host catalyst. However, this property simultaneously restricts electron release. Both effects are enhanced with an increasing capacitance value, implying that excessively high capacitance can significantly hinder the photocatalytic hydrogen (H2) production reaction. Herein, we have designed a metal-organic framework (MOF) -derived carbon-coated nickel phosphide (C-Ni5P4) as the co-catalyst of cadmium sulfide (CdS). When C-Ni5P4 and CdS are closely interconnected, electrons spontaneously migrate from CdS to C-Ni5P4 under irradiation due to the higher work function (WF) of C-Ni5P4 compared to CdS. Most importantly, although the WF of C-Ni5P4 is 0.1 eV lower than that of Ni5P4, its specific capacitance (1.2 mF/cm2) is also lower than that of Ni5P4 (1.3 mF/cm2). This difference dramatically promotes electron release. Thereby exerting a strong positive effect on capacitance catalysis. Therefore, 7% C-Ni5P4/CdS exhibits exceptional cyclic stability and has a remarkably high activity level of 12283 µmol/h/g and 3.8 times as many as 3.0 %Ni5P4/CdS. This study provides a theoretical basis for the advancement of photocatalysts with high efficiency in H2 production and is expected to be applied in other fields of photocatalysis.

Insight into the whole characteristics of (Pd/WP)/CdS for photocatalytic hydrogen evolution.

The (noble metal/non-noble metal)/semiconductor are efficient and attractive ternary photocatalysts for photocatalytic hydrogen evolution. To deeply understand the advantages of ternary photocatalysts, the physicochemical characteristics of both the whole ternary photocatalysts and each part of that must be revealed. Herein, we design (Pd/WP) as a co-catalyst loaded on CdS to form ternary photocatalysts (Pd/WP)/CdS. The (0.05%Pd/4%WP)/CdS exhibits a high hydrogen evolution activity of 18.0 mmol/h/g, which is 1.5 times of WP/CdS, 2.2 times of Pd/CdS, and 6.4 times of pure CdS. Additionally, photoelectrochemical tests demonstrate that (Pd/WP)/CdS has appropriate capacitance, excellent conductivity and strong catalytic ability, which can inhibit the recombination of photo-excited carries and boost hydrogen evolution. Especially, ultraviolet photoelectron spectroscopy (UPS) tests show that the conduction band (CB) position of (Pd/WP)/CdS can be regulated successfully through synergistic effect of Pd, WP, and CdS. This study not only reveals the physicochemical properties of ternary photocatalysts from a holistic perspective, but also provides a pathway for hydrogen evolution of scientific and economic interest.