among Ni 2 P, Ni 5 P 4 , and Ni 12 P 5 , the Ni 5 P 4 displays the best catalytic activity due to
its high P content (44%) (Fig. 16.8a). Similarly, Schaak et al. [58] synthesized
morphologically equivalent Co 2 P and CoP hollow nanoparticles by adjusting reaction time (Fig. 16.8b–d). The result showed that CoP nanoparticles have greatly
decreased the overpotential than Co 2 P to produce the same current density
(Fig. 16.8e). Furthermore, the same result could be obtained from the hydrogen
evolution between Mo 3 P and MoP [55]. All abovementioned experiments indicate a
same result that TMPs with higher P content would demonstrate better performance
in hydrogen evolution reactions.
16.3.3 Conductivity
With P atoms coupling with metal, electrically conductive metals change to
semiconductive. The P atoms with more electronegativity can strongly restrict the
electron delocalization in metal, thus lowering the conductivity [59]. Through
adjusting the difference in electronegativity and atomic ratio of metal/P, TMPs can
exhibit metallic character and even superconductivity, especially for metal-rich
phosphides. Mar et al. [60] pointed out that the di- and tri-metal phosphides show
the same electronic structure with the corresponding pure metal, confirming the
excellent conductivity of these TMPs. Based on this consideration, TMPs with
higher metal content have the better conductivity. However, as mentioned in Sect.
16.3.2, TMPs with higher P content may perform more excellent activity in hydrogen evolution reactions. Obviously, these two just contradict to each other, that is,
activity and conductivity, and we cannot have both of them. To this end, some
substances with outstanding conductivity, such as graphene [61], carbon nanotubes
[46], and carbon clothes [62], are introduced to improve the conductivity of TMPs.
16.4 Applications of TMPs in Photocatalytic Hydrogen
Evolution Reactions
16.4.1 The Origin of TMPs Acted As Cocatalysts
in Photocatalytic Hydrogen Evolution Reactions
The discovery of TMPs dates back to the last century. However, due to the limitation
of theory and technology, no obvious applications of TMPs can be observed for the
following days. The recent research studies of TMPs mainly focus on
electrocatalytic hydrogen evolution. In 2005, Liu and his coworkers [54] employed
density functional theory (DFT) to predict that Ni 2 P is a promising candidate for the
electrocatalytic hydrogen evolution. This prediction is based on the theoretical
calculation that strong H–Ni interaction on Ni 2 P (001) can lead to poisoning of the
16.4 Applications of TMPs in Photocatalytic Hydrogen Evolution Reactions
387
its high P content (44%) (Fig. 16.8a). Similarly, Schaak et al. [58] synthesized
morphologically equivalent Co 2 P and CoP hollow nanoparticles by adjusting reaction time (Fig. 16.8b–d). The result showed that CoP nanoparticles have greatly
decreased the overpotential than Co 2 P to produce the same current density
(Fig. 16.8e). Furthermore, the same result could be obtained from the hydrogen
evolution between Mo 3 P and MoP [55]. All abovementioned experiments indicate a
same result that TMPs with higher P content would demonstrate better performance
in hydrogen evolution reactions.
16.3.3 Conductivity
With P atoms coupling with metal, electrically conductive metals change to
semiconductive. The P atoms with more electronegativity can strongly restrict the
electron delocalization in metal, thus lowering the conductivity [59]. Through
adjusting the difference in electronegativity and atomic ratio of metal/P, TMPs can
exhibit metallic character and even superconductivity, especially for metal-rich
phosphides. Mar et al. [60] pointed out that the di- and tri-metal phosphides show
the same electronic structure with the corresponding pure metal, confirming the
excellent conductivity of these TMPs. Based on this consideration, TMPs with
higher metal content have the better conductivity. However, as mentioned in Sect.
16.3.2, TMPs with higher P content may perform more excellent activity in hydrogen evolution reactions. Obviously, these two just contradict to each other, that is,
activity and conductivity, and we cannot have both of them. To this end, some
substances with outstanding conductivity, such as graphene [61], carbon nanotubes
[46], and carbon clothes [62], are introduced to improve the conductivity of TMPs.
16.4 Applications of TMPs in Photocatalytic Hydrogen
Evolution Reactions
16.4.1 The Origin of TMPs Acted As Cocatalysts
in Photocatalytic Hydrogen Evolution Reactions
The discovery of TMPs dates back to the last century. However, due to the limitation
of theory and technology, no obvious applications of TMPs can be observed for the
following days. The recent research studies of TMPs mainly focus on
electrocatalytic hydrogen evolution. In 2005, Liu and his coworkers [54] employed
density functional theory (DFT) to predict that Ni 2 P is a promising candidate for the
electrocatalytic hydrogen evolution. This prediction is based on the theoretical
calculation that strong H–Ni interaction on Ni 2 P (001) can lead to poisoning of the
16.4 Applications of TMPs in Photocatalytic Hydrogen Evolution Reactions
387