Artificial　photosynthesis　is　an　ideal　method　for　solar-to-chemical　energy　conversion,　wherein　solar　energy　is　stored　in　the　form　of　chemical　bonds　of　solar　fuels.　In　particular,　the　photocatalytic　reduction　of　CO2　has　attracted　considerable　attention　due　to　its　dual　benefits　of　fossil　fuel　production　and　CO2　pollution　reduction.　However,　CO2　is　a　comparatively　stable　molecule　and　its　photoreduction　is　thermodynamically　and　kinetically　challenging.　Thus,　the　photocatalytic　efficiency　of　CO2　reduction　is　far　below　the　level　of　industrial　applications.　Therefore,　development　of　low-cost　cocatalysts　is　crucial　for　significantly　decreasing　the　activation　energy　of　CO2　to　achieving　efficient　photocatalytic　CO2　reduction.　Herein,　we　have　reported　the　use　of　a　Ni2P　material　that　can　serve　as　a　robust　cocatalyst　by　cooperating　with　a　photosensitizer　for　the　photoconversion　of　CO2.　An　effective　strategy　for　engineering　Ni-2P　in　an　ultrathin　layered　structure　has　been　proposed　to　improve　the　CO2　adsorption　capability　and　decrease　the　CO2　activation　energy,　resulting　in　efficient　CO2　reduction.　A　series　of　physicochemical　characterizations　including　X-ray　diffraction　(XRD),　X-ray　photoelectron　spectroscopy　(XPS),　transmission　electron　microscopy　(TEM),　high-resolution　transmission　electron　microscopy　(HRTEM),　and　atomic　force　microscopy　(AFM)　were　used　to　demonstrate　the　successful　preparation　of　ultrathin　Ni2P　nanosheets.　The　XRD　and　XPS　results　confirm　the　successful　synthesis　of　Ni2P　from　Ni(OH)(2)　by　a　low　temperature　phosphidation　process.　According　to　the　TEM　images,　the　prepared　Ni2P　nanosheets　exhibit　a　2D　and　near-transparent　sheet-like　structure,　suggesting　their　ultrathin　thickness.　The　AFM　images　further　demonstrated　this　result　and　also　showed　that　the　height　of　the　Ni2P　nanosheets　is　ca　1.5　nm.　The　photoluminescence　(PL)　spectroscopy　results　revealed　that　the　Ni2P　material　could　efficiently　promote　the　separation　of　the　photogenerated　electrons　and　holes　in　[Ru(bpy)(3)]Cl-2　center　dot　6H(2)O.　More　importantly,　the　Ni2P　nanosheets　could　more　efficiently　promote　the　charge　transfer　and　charge　separation　rate　of　[Ru(bpy)(3)]Cl-2　center　dot　6H(2)O　compared　with　the　Ni2P　particles.　In　addition,　the　electrochemical　experiments　revealed　that　the　Ni2P　nanosheets,　with　their　high　active　surface　area　and　charge　conductivity,　can　provide　more　active　centers　for　CO2　conversion　and　accelerate　the　interfacial　reaction　dynamics.　These　results　strongly　suggest　that　the　Ni2P　nanosheets　are　a　promising　material　for　photocatalytic　CO2　reduction,　and　can　achieve　a　CO　generation　rate　of　64.8　mu　mol.h(-1),　which　is　4.4　times　higher　than　that　of　the　Ni2P　particles.　In　addition,　the　XRD　and　XPS　measurements　of　the　used　Ni2P　nanosheets　after　the　six　cycles　of　the　photocatalytic　CO2　reduction　reaction　demonstrated　their　high　stability.　Overall,　this　study　offers　a　new　function　for　the　2D　transition-metal　phosphide　catalysts　in　photocatalytic　CO2　reduction.