  Photocatalytic water splitting is a promising renewable energy source as an
alternative for limited fossil fuels. The effectiveness of the conversion from
solar energy to hydrogen fuel relies primarily on the material. Previously,
researchers studied different TMDs such as WS$_{2}$, and PdSe$_{2}$. These
materials perform well in certain aspects such as strong adsorption stability
and promising abilities for HER, however, their band gaps are still not ideal.
In this paper, we studied a new TMD material WSe$_{2}$, which is currently used
in heterostructure photocatalysts. To our knowledge, this is the first
assessment of using transition metal doped WSe$_{2}$ as potential
photocatalysts for photocatalytic water splitting. Using first principles
calculations, we evaluated the band gaps and other photocatalytic abilities of
pristine WSe2 as well as Cr, Mo, Ta, and Re doped WSe$_{2}$. Compared to
previously studied TMD materials, three of our newly studied materials
(pristine, Mo doped, and Ta doped WSe$_{2}$)demonstrated more desirable band
gaps, which are closer to being ideal (1.23eV); The band edge positions of our
materials are also closer to the ideal reduction potential of H$^{+}$/H$_{2}$
and the oxidation potential of O$_{2}$/H$_{2}$O. Furthermore, Mo and Ta doped
WSe$_{2}$ monolayers undergo an exothermic process, indicating stable
monolayers. Of the three selected materials, pristine WSe$_{2}$ exhibits the
strongest water adsorption abilities. Our results substantiates pristine, Mo
doped, and Cr doped WSe$_{2}$ as potential photocatalysts for water splitting.
