ZrZnO x is active in catalyzing carbon dioxide (CO 2 ) hydrogenation to methanol (MeOH) via a synergy between ZnO x and ZrO x . Here we report the construction of Zn 2+ −O−Zr 4+ sites in a metal−organic framework (MOF) to reveal insights into the structural requirement for MeOH production. The Zn 2+ −O−Zr 4+ sites are obtained by postsynthetic treatment of Zr 6 (μ 3 -O) 4 (μ 3 -OH) 4 nodes of MOF-808 by ZnEt 2 and a mild thermal treatment to remove capping ligands and afford exposed metal sites for catalysis. The resultant MOF-808-Zn catalyst exhibits >99% MeOH selectivity in CO 2 hydrogenation at 250 °C and a high space-time yield of up to 190.7 mg MeOH g Zn −1 h −1 . The catalytic activity is stable for at least 100 h. X-ray absorption spectroscopy (XAS) analyses indicate the presence of Zn 2+ −O−Zr 4+ centers instead of Zn m O n clusters. Temperature-programmed desorption (TPD) of hydrogen and H/D exchange tests show the activation of H 2 by Zn 2+ centers. Open Zr 4+ sites are also critical, as Zn 2+ centers supported on Zr-based nodes of other MOFs without open Zr 4+ sites fail to produce MeOH. TPD of CO 2 reveals the importance of bicarbonate decomposition under reaction conditions in generating open Zr 4+ sites for CO 2 activation. The welldefined local structures of metal-oxo nodes in MOFs provide a unique opportunity to elucidate structural details of bifunctional catalytic centers.

Hydrogenation of carbon dioxide (CO 2 ) to ethylene (C 2 H 4 ) can be achieved in two routes via tandem reactions: (1) CO 2 hydrogenation to methanol (CH 3 OH) followed by methanol-to-olefin conversion and (2) reverse water-gas shift reaction followed by Fischer−Tropsch synthesis. Here we present another tandem route for CO 2 -to-C 2 H 4 conversion via (3) CO 2 hydrogenation to ethanol (C 2 H 5 OH) followed by C 2 H 5 OH dehydration. Multiple cuprous (Cu I ) centers were loaded onto the Ti 8 (μ 2 -O) 8 (μ 2 -OH) 4 secondary building units of a Ti-based metal−organic framework (MOF), MIL-125-NH 2 , via deprotonation and ion exchange of the μ 2 -OH groups. These multiple Cu I centers catalyzed CO 2 hydrogenation to C 2 H 5 OH, while the Ti 2 -μ 2 -O − M + (M + = H + , Li + ) sites converted C 2 H 5 OH to C 2 H 4 . The MOF achieved CO 2 -to-C 2 H 4 generation rates of up to 2598 μmol g Cat −1 h −1 in supercritical CO 2 (CO 2 30 MPa, H 2 5 MPa) at 85 °C and 514 μmol g Cat −1 h −1 in the gas phase at 5 MPa (H 2 :CO 2 = 3) and 100 °C, respectively. This work opens another path to selectively producing C 2 H 4 via the hydrogenation of CO 2 .

PbTiO 3 (PTO) is explored as a versatile and tunable electron-selective layer (ESL) for perovskite solar cells. To demonstrate effectiveness of PTO for electron-hole separation and charge transfer, perovskite solar cells are designed and fabricated in the laboratory with the PTO as the ESL. The cells achieve a power conversion efficiency (PCE) of ≈12.28% upon preliminary optimization. It is found that the PTO ferroelectric layer can not only increase the PCE, but also tune the photocurrent via tuning PTO's ferroelectric polarization. Moreover, to understand the physical mechanism underlying the carrier transport by the ferroelectric polarization, the electronic structure of PTO/CH 3 NH 3 PbI 3 heterostructure is computed using the first-principles methods, for which the triplet state is used to simulate charge transfer in the heterostructure. It is shown that the synergistic effect of type II band alignment and the specific ferroelectric polarization direction provide the effective extraction of electrons from the light absorber, while minimize recombination of photogenerated electronhole pairs. Overall, the ferroelectric PTO is a promising and tunable ESL for optimizing electron transport in the perovskite solar cells. The design offers a different strategy for altering direction of carrier transport in solar cells.

Functionalized graphene is widely used in various functional devices. Here, we introduce a simple plane capacity model and the density functional theory to investigate the origin of charge transfer in the graphene/CH 3 NH 3 PbI 3 interface, where graphene can be p-type or n-type doped by combining with different exposed surfaces of CH 3 NH 3 PbI 3 . Our calculations indicate that at the equilibrium distance, the work function of isolated graphene layer should be corrected by adding a value for assessing the charge transfer. After integrating the perovskite film with the functionalized graphene layer, we obtain a van der Waals heterostructure solar cell with a p−i−n configuration, which introduces a built-in electrical field to facilitate the separation and transport of the photogenerated carriers. The new p−i−n junction highlights the interface effect on graphene in solar cell, which offers an avenue to design new photovoltaic devices with high performance.