Sunlight plays a critical role in the development of emerging sustainable energy conversion and storage technologies. Light-induced CO2 reduction by artificial photosynthesis is one of the cornerstones to produce renewable fuels and environmentally friendly chemicals. Interface interactions between plasmonic metal nanoparticles and semiconductors exhibit improved photoactivities under a wide range of the solar spectrum. However, the photo-induced charge transfer processes and their influence on photocatalysis with these materials are still under debate, mainly due to the complexity of the involved routes occurring at different timescales. Here, we use a combination of advanced in situ and time-resolved spectroscopies covering different timescales, combined with theoretical calculations, to unravel the overall mechanism of photocatalytic CO2 reduction by Ag/TiO2 catalysts. Our findings provide evidence of the key factors determining the enhancement of photoactivity under ultraviolet and visible irradiation, which have important implications for the design of solar energy conversion materials.

Despite nearly 40 years of research on CO 2 photocatalytic reduction and the increasing number of works dealing with this application, there are still many unknowns on the mechanistic aspect of the reaction.Perspective pubs.acs.org/JPCL

poor applicability for movable applications. Therefore, the development of new technologies to store renewable energy is really important to achieve the transition to a greener energy system. [3] Although new battery technologies will likely meet the need for cost-effective energy storage (1-3 days) for short time scales, fuels are the only effective option for longerterm, seasonal storage, and long-distance transportation applications. [4] Collecting and loading solar energy into electric power and more interestingly directly into valuable chemicals and fuels, as nature does through photosynthesis, is a highly desirable approach to solve this challenge. Since Honda and Fujishima [5] discovered the possibility to emulate this natural phenomenon using TiO 2 as photocatalyst more than 40 years ago, the scientific community has been trying to overcome the challenges hindering the commercialization of water splitting and CO 2 reduction. [6,7] During the past years, a large variety of systems have been proposed to drive the so-called artificial photosynthesis (AP), most of them based on inorganic semiconductors (ISs), usually metal oxides and metal chalcogenides. IS are able to absorb part of the solar spectrum and promote charge separation into electron and holes. In fact, there is a lot of recent work in the literature reviewing the use of ISs as photoabsorbers in photocatalytic, photoelectrochemical (PEC), and photovoltaic (PV) systems. [8,9] The achievements and improvements performed in this area have been always enormous. In this sense, among the huge number of materials explored, TiO 2 has been by far the most investigated until now due to its unique properties: high photoactivity and chemical stability, availability, and nontoxicity. [10,11] However, some ISs, and TiO 2 in particular, present well-known shortcomings in terms of low light absorption in the visible part of solar spectrum and fast charge recombination that limits electron donor-acceptor process. Therefore, the energy conversion efficiency achieved until now is still low. The improvement of this efficiency relies on the use of new materials that are able to harvest solar light and active toward CO 2 /N 2 reduction and water splitting. The most successful strategies to improve the photocatalyst performance so far have been: i) the modification of the optoelectronic properties of TiO 2 or other ISs, [12] ii) the use of organic materials as semiconductors, Solar energy conversion plays a very important role in the transition to a more sustainable energy system. In this sense, so many systems have been proposed to drive artificial photosynthesis, most of them based on inorganic semiconductors, and the achievements performed continue every day. However, most of these systems present well-known shortcomings as low light absorption, fast charge recombination, and lack of tunability, thus limiting their efficiency. The use of organic polymers in general and conjugated porous polymers (CPPs) in particular, opens the door to a multitude of new possibilities...

Developing highly efficient photocatalysts for artificial photosynthesis is one of the grand challenges in solar energy conversion. Among advanced photoactive materials, conjugated porous polymers (CPPs) possess a powerful combination of high surface areas, intrinsic porosity, cross‐linked nature, and fully π‐conjugated electronic systems. Here, based on these fascinating properties, organic–inorganic hybrid heterostructures composed of CPPs and TiO2 for the photocatalytic CO2 reduction and H2 evolution from water are developed. The study is focused on CPPs based on the boron dipyrromethene (BODIPY) and boron pyrrol hydrazine (BOPHY) families of compounds. It is shown that hybrid photocatalysts are active for the conversion of CO2 mainly into CH4 and CO, with CH4 production 4 times over the benchmark TiO2. Hydrogen evolution from water surpassed by 37.9‐times that of TiO2, reaching 200 mmol gcat−1 and photonic efficiency of 20.4% in the presence of Pt co‐catalyst (1 wt% Pt). Advanced photophysical studies, based on time‐resolved photoluminescence and transient absorption spectroscopy, reveal the creation of a type II heterojunction in the hybrids. The unique interfacial interaction between CPPs and TiO2 results in longer carriers’ lifetimes and a higher driving force for electron transfer, opening the door to a new generation of photocatalysts for artificial photosynthesis.