Immobilization of Re­(I) CO2 reduction photocatalysts on metal oxide surfaces is an interesting approach to improve their stability and recyclability. In this work, we describe the photocatalytic activity of two Re­(I) complexes (fac-[Re­(NN)­(CO)3(Cl)], NN = 4,4'-dicarboxylic acid-2,2'-bipyridine, 1, or 5,6-dione-1,10-phenantroline, 2) on the surface of hexaniobate nanoscrolls. After adsorption, the turnover number for CO production (TONCO) in DMF/TEOA of 1 was increased from 9 to 58, which is 20% higher than that observed on TiO2, being among the highest reported values for a Re­(I)-based photocatalyst under visible light irradiation without any sensitizer. The complex 2 is inactive in solution under visible-light irradiation, but it has a TONCO of 35 when immobilized on hexaniobate nanoscrolls. Transient absorption spectroscopy studies reveal that the slow back-electron transfer and the higher reducing power of the hexaniobate conduction-band electrons play a major role for the photocatalytic process. The results provide new insights concerning the role of the metal oxide substrate on Re­(I)-based molecular systems for CO2 reduction.

The large and continuous use of fossil fuels as a primary energy source has led to several environmental problems, such as the increase of the greenhouse effect. In order to minimize these problems, attention has been drawn to renewable energy production. Solar energy is an attractive candidate as renewable source due to its abundance and availability. For this, it is necessary to develop devices able to absorb sunlight and convert it into fuels or electricity in a economical, technical and sustainable way. The so-called artificial photosynthesis has called the attention of researchers due to the possibility of using solar photocatalysts in converting water and CO2 into fuels. This manuscript presents a review of the recent developments of hybrid systems based on molecular photocatalysts immobilized on semiconductor surfaces for solar fuel production through water oxidation and CO2 reduction and also discusses the current challenges for the potential application of these photocatalyst systems.

A novel Re(i) complex with a thiosemicarbazone derivative is described and fully characterized. Its was further explored as CO2 reduction electrocatalyst, being the first complex with a thiosemicarbazone derivative applied to this goal.

The Nobel Prize in Chemistry 2019 recognized the importance of Li-ion batteries and the revolution they allowed to happen during the past three decades. They are part of a broader class of electrochemical energy storage devices, which are employed where electrical energy is needed on demand and so, the electrochemical energy is converted into electrical energy as required by the application. This opens a variety of possibilities on the utilization of energy storage devices, beyond the well-known mobile applications, assisting on the decarbonization of energy production and distribution. In this series of reviews in two parts, two main types of energy storage devices will be explored: electrochemical capacitors (part I) and rechargeable batteries (part II). More specifi cally, we will discuss about the materials used in each type of device, their main role in the energy storage process, their advantages and drawbacks and, especially, strategies to improve their performance. In the present part, electrochemical capacitors will be addressed. Their fundamental difference to batteries is explained considering the process at the electrode/electrolyte surface and the impact in performance. Materials used in electrochemical capacitors, including double layer capacitors and pseudocapacitive materials will be reviewed, highlighting the importance of electrolytes. As an important part of these strategies, synthetic routes for the production of nanoparticles will also be approached (part I).

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In the second part of the review on electrochemical energy storage, the devolvement of batteries is explored. First, fundamental aspects of battery operation will be given, then, different materials and chemistry of rechargeable batteries will be explored, including each component of the cell. In negative electrodes, metallic, intercalation and transformation materials will be addressed. Examples are Li or Na metal batteries, graphite and other carbonaceous materials (such as graphene) for intercalation of metal-ions and transition metal oxides and silicon for transformation.In the positive electrode section, materials for intercalation and transformation will be reviewed. The state-of-the-art on intercalation as lithium cobalt oxide and nickel containing oxides will be approached for intercalation materials, whereas sulfur and metal-air will also be explored for transformation. Alongside, the role of electrolyte will be discussed concerning performance and safety, with examples for the next generation devices. Finally, a general future perspective will address both electrochemical capacitors and batteries.

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