The
design of materials meeting the rigorous requirements of photocatalytic
water splitting is still a challenge. Anisotropic Janus 2D materials
exhibit great potential due to outstandingly high photocatalytic efficiency.
Unfortunately, these materials are scarce. By means of ab initio swarm-intelligence
search calculations, we identify a SiP
2
monolayer with
Janus structure (i.e., out-of-plane asymmetry). The material turns
out to be semiconducting with an indirect band gap of 2.39 eV enclosing
the redox potentials of water. Notably, the oxygen and hydrogen evolution
half reactions can happen simultaneously at the Si and P atoms, respectively,
driven merely by the radiation-induced electrons and holes. The carrier
mobility is found to be anisotropic and high, up to 10
–4
cm
2
V
–1
s
–1
, facilitating
fast transport of the photogenerated carriers. The SiP
2
monolayer shows remarkably strong optical absorption in the visible-to-ultraviolet
range of the solar spectrum, ensuring efficient utilization of the
solar energy.