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.

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.

This work proposes the use of albedo of orange peel in generation of carbon for applications in supercapacitors. For this, a comparison of compositional and electrochemical properties present in the carbons obtained of albedo, flavedo, and the complete orange peel was carried out. The morphology and composition of carbons obtained were analyzed by Field Emission Scanning Electron Microscopy (FESEM), Energy Dispersive X-ray (EDX), X-Ray Diffraction (XRD), and Fourier-transform infrared spectroscopy (FT-IR). The synthetized carbons were not subjected to the activation process by chemical compounds to relate only the properties of orange peel parts with their electrochemical behaviour. All samples were tested by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). The carbon obtained of albedo presented a superior specific capacitance (210 F/g) of the rest samples. The value of albedo-based carbon capacitance is comparable with works presented in the literature that used a whole orange peel with chemical activators. In this way, it is possible to obtain large capacitances using only a part of orange peel (albedo). Thus, the importance of this study is that the albedo can be proposed as a material applied to electrodes for supercapacitors while the flavedo can be used in food industry or for oil extraction.

The most widely used support in low-temperature fuel cell applications is the commercially available Vulcan XC-72. Herein, we report its functionalization with the home-obtained mesityl copper (Cu-mes) and Cu coordinate (Cu(dmpz)L2) organometallic compounds. Pd nanoparticles are anchored on the supports obtaining Pd/C_Cu-mes, Pd/C_Cu(dmpz)L2, and Pd/C (on nonfunctionalized support). The polarization curves of the ethanol oxidation reaction (EOR) show that Pd/C_Cu-mes and Pd/C_Cu(dmpz)L2 promote the reaction at a more negative onset potential, i.e., E _onset = 0.38 V/reversible hydrogen electrode (RHE), compared to 0.41 V/RHE of Pd/C. The mass current density (j _m) delivered by Pd/C_Cu-mes is considerably higher (1231.3 mA mg_Pd ^-1), followed by Pd/C_Cu(dmpz)L2 (1001.8 mA mg_Pd ^-1), and Pd/C (808.3 mA mg_Pd ^-1). The enhanced performance of Pd/C_Cu-mes and Pd/C_Cu(dmpz)L2 for the EOR (and tolerance to CO poisoning) is attributed to a shift of their d-band center toward more negative values, compared to Pd/C, because of the formation of PdCu alloyed phases arising from the functionalization. In addition, laboratory-scale tests of the anion exchange membrane-direct ethanol fuel cell assembled with Pd/C_Cu-mes show the highest open circuit voltage (OCV = 0.60 V) and cell power density (P _cell = 0.14 mW cm^-2). As a result of its high catalytic activity, Pd/C_Cu-mes can find application as an anode nanocatalyst in AEM-DEFCs.

Borocarbonitrides (BCNs), a new class of ternary materials combining boron, carbon, and nitrogen atoms, have emerged as promising candidates in decarbonization technologies due to their unique physicochemical properties. BCNs offer an adjustable atom composition and electronic structure, thermal stability, and potentially a large specific surface area, which are attractive features for efficient interactions with carbon dioxide. These make BCNs suitable for carbon dioxide capture, storage, and catalytic conversion applications. Furthermore, BCNs have the potential to (electro)catalyze the synthesis of green fuels, such as hydrogen, as well as that of other hydrogen carriers such as ammonia. With this review, we examine the recent advances in BCN synthesis methods, characterization, and functional applications while focusing on their role in the decarbonization technologies mentioned above. We aim to highlight the potential of BCNs to drive innovation in sustainable carbon management. Additionally, in the last section of this paper, we discuss the challenges and prospects of BCNs in decarbonization and beyond.