Density functional theory calculations have been performed to investigate the structural, electronic, and CO_2 adsorption properties of 55-atom bimetallic Cu Ni nanoparticles(NPs) in core-shell and decorated architectures,as well as of their monometallic counterparts. Our results revealed that with respect to the monometallic Cu_(55) and Ni55parents, the formation of decorated Cu_(12)Ni_(43) and core-shell Cu_(42)Ni_(13) are energetically favorable. We found that CO_2 chemisorbs on monometallic Ni_(55), core-shell Cu_(13)Ni_(42), and decorated Cu_(12)Ni_(43) and Cu_(43)Ni_(12),whereas, it physisorbs on monometallic Cu_(55) and core-shell Cu_(42)Ni_(13). The presence of surface Ni on the NPs is key in strongly adsorbing and activating the CO_2 molecule(linear to bent transition and elongation of C~=O bonds). This activation occurs through a charge transfer from the NPs to the CO_2 molecule, where the local metal d-orbital density localization on surface Ni plays a pivotal role. This work identifies insightful structureproperty relationships for CO_2 activation and highlights the importance of keeping a balance between NP stability and CO_2 adsorption behavior in designing catalytic bimetallic NPs that activate CO_2. Density functional theory designs have been performed to investigate the structural, electronic, and CO_2 adsorption properties of 55-atom bimetallic Cu Ni nanoparticles (NPs) in core-shell and decorated architectures, as well as their monometallic counterparts. Our results revealed that with We found that CO_2 chemisorbs on monometallic Ni_ (55) and Ni_55parents, the formation of decorated Cu_ (12) Ni_ (43) and core-shell Cu_ (42) Ni_ (13) are energetically favorable. , core-shell Cu_ (13) Ni_ (42), and decorated Cu_ (12) Ni_ (43) and Cu_ (43) Ni_ (12) The presence of surface Ni on the NPs is key strongly adsorbing and activating the CO 2 molecule (linear to bent transition and elongation of C ~ = O bonds). This activation occurs through a charge transfer from the NPs to the CO_2 molecule, where the local metal d-orbital density localization on surface Ni plays a pivotal role. This wor k identifies insightful structureproperty relationships for CO 2 activation and highlights the importance of keeping a balance between NP stability and CO_2 adsorption behavior in designing catalytic bimetallic NPs that activate CO_2.