Water splitting technology is an innovative strategy to face the dependency on fossil fuels and, at the same time, address environmental pollution issues. Electrocatalysts seem to be the better option to improve water separation efficiency and satisfy the commercial-scale demand for hydrogen. Therefore, the design and fabrication of heterostructures with a high affinity for achieving water splitting have been proposed. In this review, the application of several electrocatalysts for hydrogen and oxygen evolution reactions is presented and discussed in detail. A review of the recent advances in water separation using noble metals such as Pt-, Ir-, and Ru-based electrodes is presented, followed by a highlighting of the current trends in noble-metal-free electrocatalysts and novel preparation methods. Furthermore, it contemplates some results of a hybrid organic molecule–water electrolysis and photoelectrochemical water splitting. This review intends to give insight into the main trends in water splitting and the barriers that need to be overcome to further boost the efficiency of the main hydrogen and oxygen generation systems that ultimately result in large-scale applications. Finally, future challenges and perspectives are addressed, considering all the novelties and the proposed pathways for water splitting.

In this paper, the potential of marine algae to act as sensitizers is systematically studied and presented. We aim to find a feasible financial strategy to enhance the global efficiency of dye-sensitized solar cells (DSSC). Algae are mainly composed of chlorophylls, carotenoids, flavonoids, and Betalains, which are essential pigments that confer unique characteristics that are required in natural sensitizers. Therefore, this review aims to unveil and understand the underlying mechanism between algae pigments and photoelectrodes and to conduct a comprehensive analysis to determine the effect of algae dye on light absorption efficiency and electron transport. The structural, morphological, optical, and electrochemical impedance properties are deeply analyzed, and we show the current opportunities for natural dyes to be used in energy technologies through DSSC. A comparison of several bibliographic sources dealing with DSSC based on algae provided a general overview of the improvements in factors such as the recombination times, the filling factor, and the Voc values. The contributions of this paper relate to the conversion efficiency and future applications in the DSSC field. Finally, this review exemplifies that the nature of the pigment affects the photophysical properties of the cell. Thus, this paper may contribute to future investigations of DSSC when choosing efficient natural dyes according to their optical and electronic properties. Therefore, this work provides the knowledge required to efficiently merge materials and dyes, in which photovoltaic energy systems’ reproducibility and scalability still represent a challenge. Lastly, this document discusses the natural pigments’ stability and the approaches to improve their chemical stability.

Currently, a large amount of pharmaceutical waste (PW) and its derivatives are being produced and, in some cases, inadequate management or treatment practices are applied. In this regard, this research explores the adoption of several alternatives to deal with these problems, including biocarbon within the framework of the circular economy. Photocatalytic nanomaterials have been also extensively discussed as a feasible way to remove pharmaceutical compounds in wastewater. Although there are existing reports in this area, this document provides a detailed study of the synthesis process, experimental conditions, the integration of photocatalysts, and their impact on enhancing photocatalytic efficiency. Additionally, the low cost and ease of fabrication of lab-scale microbial fuel cells (MFCs) are thoroughly examined. This innovative technology not only facilitates the degradation of hazardous compounds in wastewater but also harnesses their energy to generate electricity simultaneously. The aforementioned approaches are covered and discussed in detail by documenting interesting recently published research and case studies worldwide. Furthermore, this research is of significant importance because it addresses the valorization of PW by generating valuable by-products, such as H₂ and O₂, which can occur simultaneously during the photodegradation process, contributing to more sustainable industrial practices and clean energy technologies.

Currently, great importance has been assigned to designing cutting-edge materials for oxygen and hydrogen generation from hybrid water electrolysis as an ideal fuel alternative in energy-conversion devices. This work reports on the electrochemical organic molecule oxidation in alkaline media, intending to promote water electrolysis at early onset potential with more current densities using Sn-Cu oxidized heterostructures. The electrocatalysts were easily and rapidly synthesized by the microwave-heated synthesis process in the presence of a small quantity of ethylene glycol. The X-ray diffraction and Field Emission Scanning Electron Microscopy analyses confirm the presence of CuO and SnO₂ phases, which significantly improves the electrochemical activity of the composite toward the Oxygen Evolution Reaction (OER) in alkaline media in the presence of 1.0 mol L⁻¹ ethanol, yielding 8.0 mA cm⁻² at 1.6 V. The charge transfer resistance (R_ct) was determined using electrochemical impedance spectroscopy, and the result shows that the R_ct of SnO₂/CuO drastically decreased. The findings in this work highlight that the designed oxidized heterostructures with non-noble metals are promising candidates for energy conversion devices and sensors. Furthermore, this work confirms the advantages of using an assisted microwave heating process to develop an advanced SnO₂/CuO composite with the potential to be used in electro-oxidation processes.

Hydrogen and oxygen serve as energy carriers that can ease the transition of energy due to their high energy densities. Nonetheless, their production processes entail the development of efficient and low-cost storage and conversion technologies. In this regard, photoelectrocatalysts are materials based on the photoelectronic effect where electrons and holes interact with H₂O, producing H₂ and O_2, and in some cases, this is achieved with acceptable efficiency. Although there are several reviews on this topic, most of them focus on traditional semiconductors, such as TiO₂ and ZnO, neglecting others, such as those based on non-noble metals and organic ones. Herein, semiconductors like CdSe, NiWO₄, Fe₂O₃, and others have been investigated and compared in terms of photocurrent density, band gap, and charge transfer resistance. In addition, this brief review aims to discuss the mechanisms of overall water-splitting reactions from a photonic point of view and subsequently discusses the engineering of material synthesis. Advanced composites are also addressed, such as WO₃/BiVO₄/Cu₂O and CN-FeNiOOH-CoOOH, which demonstrate high efficiency by delivering photocurrent densities of 5 mAcm⁻² and 3.5 mA cm⁻² at 1.23 vs. RHE, respectively. Finally, the authors offer their perspectives and list the main challenges based on their experience in developing semiconductor-based materials applied in several fields. In this manner, this brief review provides the main advances in these topics, used as references for new directions in designing active materials for photoelectrocatalytic water splitting.

In the present work, photoanodes for dye-sensitised solar cell (DSSC) composed of SnO₂ nanoparticles were developed by electrophoretic deposition (EPD) process . Taguchi experimental design was adopted to investigate the effect of EPD parameters into the physical and chemical properties of the deposited film. The deposited photoanodes were characterized by scanning electron microscopy (SEM) and optical microscope. Also, electrical measurements were conducted with the aim to evaluate the effect of the deposition parameters on the DSSC current density. The experimental results reveal that magnesium nitrate concentration has the most significant effect on the photocurrent densities followed by the time of deposition. It has been observed that the deposition parameters studied greatly influence the morphology of the obtained film. This indicates that the electrophoretic deposition process under a Taguchi design orthogonal array might be a cost efficient method to develop anodes for DSSC.