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The increasing demand for energy and the environmental challenges posed by fossil fuel consumption prompts the exploration of clean and sustainable energy solutions. This review article focuses on the innovative approach of generating energy through the electrolysis of wastewater, which not only facilitates clean energy production but also aids in wastewater treatment. Significant advancements in electrooxidation processes for the sustainable production of hydrogen and other valuable chemicals are highlighted. This article specifically analyzes the techno‐economic aspects of electrooxidation for small molecules, including alcohol, amine, hydrazine, iodine, and urea, within the framework of wastewater treatment. Cost estimations for hydrogen and value‐added products derived from the oxidation reactions are presented, with production costs calculated at$6.37, $ 6.06,$2.68, $ 5.69, and $10.69 per kilogram of H2, respectively. However, the costs associated with alcohol oxidation reactions and urea oxidation reactions are deemed unfeasible. An analysis of profitability reveals that the oxidation processes for iodine, hydrazine, and amine wastewater generate revenue profits of 28%, 16%, and 6%, respectively. There is increasing worry regarding the environmental impact of waste from hospital sewage, agricultural runoff, and industrial wastewater. Those wastes can contaminate water ecosystems, harming both human health and aquatic life. By employing an electrochemical method, we can treat these toxic substances in wastewater while simultaneously producing hydrogen gas and other valuable byproducts, which can generate income.

Hybrid water splitting, using methanol or ethanol oxidation reactions (MOR and EOR) at the counter electrode during electrochemical hydrogen generation, offers an efficient alternative to the sluggish oxygen evolution reaction (OER). This study reports Cu/Co‐based core‐shell nanocrystals (NCs) showing excellent performance for both MOR and EOR. The structure, composition and size of the NCs can be controlled by adjusting the synthesis parameters in a one‐pot microwave‐assisted process. The electrocatalytic performance of the NCs shows lower potentials for both MOR and EOR compared to the OER. They consist of a copper‐rich metallic core initially encapsulated by a shell composed of cobalt oxide and cobalt carbide. This nanoheterostructure evolves to a copper oxide core surrounded by an oxide shell consisting of small cobalt‐ and copper‐oxide nanodomains upon chronopotentiometry experiments. The excellent performance in both MOR and EOR is attributed to the oxidation of the NCs and a concomitant diffusion process that forms small oxide clusters. The final structure provided NCs with high mass activities for both alcohol oxidation reactions, producing formic and acetic acid as products (for MOR and EOR, respectively). Finally, the NCs are tested for hybrid water electrolysis, demonstrating high hydrogen production along with high stability. Cu/Co‐based core‐shell nanocrystals (NCs) enable efficient hybrid water splitting via methanol and ethanol oxidation (MOR and EOR), outperforming traditional oxygen evolution reaction (OER). Synthesized via a one‐pot microwave process, the NCs evolve into oxide clusters that deliver high electrocatalytic activity and stability, enabling effective hydrogen production and yielding formic and acetic acids from MOR and EOR, respectively.

The potential of metal oxides in electrochemical energy storage encouraged our research team to synthesize molybdenum oxide/tungsten oxide nanocomposites (MoO 3 /WO 3 ) and their hybrid with reduced graphene oxide (rGO), in the form of MoO 3 /WO 3 /rGO as a substrate with relatively good electrical conductivity and suitable electrochemical active surface. In this context, we presented the electrochemical behavior of these nanocomposites as an electrode for supercapacitors and as a catalyst in the oxidation process of methanol/ethanol. Our engineered samples were characterized by X-ray diffraction pattern and scanning electron microscopy. As a result, MoO 3 /WO 3 and MoO 3 /WO 3 /rGO indicated specific capacitances of 452 and 583 F/g and stability of 88.9% and 92.6% after 2000 consecutive GCD cycles, respectively. Also, MoO 3 /WO 3 and MoO 3 /WO 3 /rGO nanocatalysts showed oxidation current densities of 117 and 170 mA/cm 2 at scan rate of 50 mV/s, and stability of 71 and 89%, respectively in chronoamperometry analysis, in the MOR process. Interestingly, in the ethanol oxidation process, corresponding oxidation current densities of 42 and 106 mA/cm 2 and stability values of 70 and 82% were achieved. MoO 3 /WO 3 and MoO 3 /WO 3 /rGO can be attractive options paving the way for prospective alcohol-based fuel cells.

The development of Pt-based core/shell nanoparticles represents an emerging class of electrocatalysts for fuel cells, such as methanol oxidation reaction (MOR) and ethanol oxidation reaction (EOR). Here, we present a one-pot synthesis approach to prepare hexagonal PtBi/Pt core/shell nanostructure composed of an intermetallic Pt 1 Bi 1 core and an ultrathin Pt shell with well-defined shape, size, and composition. The structure and the synergistic effect among different components enhanced their MOR and EOR performance. The optimized Pt 2 Bi nanoplates exhibit excellent mass activities in both MOR (4,820 mA·mgPt –1 ) and EOR (5,950 mA·mgPt –1 ) conducted in alkaline media, which are 6.15 times and 8.63 times higher than those of commercial Pt/C, respectively. Pt 2 Bi nanoplates also show superior operation durability to commercial Pt/C. This work may inspire the rational design and synthesis of Pt-based nanoparticles with improved performance for fuel cells and other applications.

Co 3 O 4 nanoneedles have been incorporated onto the layers of graphene oxide (Co 3 O 4 NN/GO) through a simple hydrothermal route. The high energy input for water electrolysis can be reduced by hybrid water electrolysis via electrolyte engineering. In this study, oxygen evolution reaction (OER) has been replaced with oxidation of nitrogen containing compounds such as urea and hydrazine (UOR and HzOR). Among transition metal oxides, spinel Co 3 O 4 exhibits switchable redox states of Co 2+ and Co 3+ . Also, its electronic conductivity is improved with GO carbon support which make it a promising electrocatalyst towards OER as well as UOR and HzOR. In this study, the Co 3 O 4 NN/GO has delivered potentials of 1.56, 1.29, and 0.043 V vs RHE at 10 mA cm −2 for OER, UOR, and HzOR in alkaline medium, respectively. The two-electrode cell constructed by employing Co 3 O 4 NN/GO as anode and Pt/C as cathode required an ultra-low cell voltage of 0.33 V for overall hydrazine-assisted water electrolysis, which was 1.32 V lower than that of a conventional alkaline water electrolyzer (1.64 V). The cost-effectiveness and simple conversion of biomass orange peel to GO under mild conditions with the incorporation of Co 3 O 4 nanoneedles have provided a new route for catalytic design with carbon supports from biomass for highly energy-efficient hybrid water electrolysis.

To enable a future society based on sun and wind energy, transforming electricity into chemical energy in the form of fuels is crucial. This transformation can be achieved in an electrolyzer performing water splitting, where at the anode, water is oxidized to oxygen—oxygen evolution reaction (OER)—to produce protons and electrons that can be combined at the cathode to form hydrogen—hydrogen evolution reaction (HER). While hydrogen is a desired fuel, the obtained oxygen has no economic value. A techno‐economically more suitable alternative is hybrid water electrolysis, where value‐added oxidation reactions of abundant organic feedstocks replace the OER. However, tremendous challenges remain for the industrial‐scale application of hybrid water electrolysis. Herein, these challenges, including the higher kinetic overpotentials of organic oxidation reactions compared to the OER, the small feedstock availably and product demand of these processes compared to the HER (and carbon dioxide reduction), additional purifications costs, and electrocatalytic challenges to meet the industrially required activities, selectivities, and especially long‐term stabilities are critically discussed. It is anticipated that this perspective helps the academic research community to identify industrially relevant research questions concerning hybrid water electrolysis. Hybrid water electrolysis has emerged as a promising field for the coproduction of hydrogen and value‐added chemicals. Herein, a short overview of the reactions investigated and the challenges to be solved to accelerate developments toward industrial‐scale applications is given.

Today, finding low-cost electro-catalysts for methanol and ethanol oxidation with high performance and stability is one of the new research topics. A nanocatalyst based on metal oxides in the form of MnMoO4 was synthesized by a hydrothermal method for methanol (MOR) and ethanol (EOR) oxidation reactions. Adding reduced graphene oxide (rGO) to the catalyst structure improved the electrocatalytic activity of MnMoO4 for the oxidation processes. The crystal structure and morphology of the MnMoO4 and MnMoO4-rGO nanocatalysts were investigated by physical analyses such as scanning electron microscopy and X-ray diffraction. Their abilities for MOR and EOR processes in an alkaline medium were evaluated by performing electrochemical tests such as cyclic voltammetry, chronoamperometry, and electrochemical impedance spectroscopy. MnMoO4-rGO showed oxidation current densities of 60.59 and 25.39 mA/cm2 and peak potentials of 0.62 and 0.67 V in MOR and EOR processes (at a scan rate of 40 mV/s), respectively. Moreover, stabilities of 91.7% in MOR and 88.6% in EOR processes were obtained from the chronoamperometry analysis within 6 h. All these features make MnMoO4-rGO a promising electrochemical catalyst for the oxidation of alcohols.

Small‐molecule electrooxidation‐boosted water electrolysis (WE) is an energy‐saving method for hydrogen (H2) production. Herein, PdPt bimetallenes (PdPt BMLs) are obtained through the simple galvanic replacement reaction. PdPt BMLs reveal 2.93‐fold enhancement in intrinsic electroactivity and 4.53‐fold enhancement in mass electroactivity for the formate oxidation reaction (FOR) with respect to Pd metallenes (Pd MLs) at 0.50 V potential due to the synergistic effect. Meanwhile, the introduction of Pt atoms also considerably increases the electroactivity of PdPt BMLs for hydrogen evolution reaction (HER) with respect to Pd MLs in an alkaline medium, which even exceeds that with the use of commercial Pt nanocrystals. Inspired by the outstanding FOR and HER electroactivity of bifunctional PdPt BMLs, a two‐electrode FOR‐boosted WE system (FOR‐WE) is constructed by using PdPt BMLs as the cathode and the anode. The FOR‐WE system only requires an operational voltage of 0.31 V to achieve H2 production, which is 1.48 V lower than that (ca. 1.79 V) with the use of the traditional WE system. PdPt bimetallenes (PdPt BMLs) are synthesized by a galvanic replacement reaction, which leads to enhancement of intrinsic electroactivity for both the formate oxidation reaction and the hydrogen evolution reaction with respect to Pd metallence due to the synergistic effect. Also, the PdPt BMLs||PdPt BMLs formate electrolyzer requires an operational voltage of only 0.31 V for H2 production, which is 1.48 V lower than that of the traditional water electrolysis system.

HighlightsTwo types of vertical 3D nanostructures were successfully fabricated using simple hydrothermal and heat treatment processes for hydrogen evolution reaction and glycerol oxidation reaction (GOR).Hydrogen production at a lower potential was achieved by replacing oxygen evolution reaction with GOR, reducing the device potential by approximately 300 mV. Additionally, organic membranes were used as separators, avoiding the use of expensive anion exchange membranes.Hydrogen production from electrolytic water is an important sustainable technology to realize renewable energy conversion and carbon neutrality. However, it is limited by the high overpotential of oxygen evolution reaction (OER) at the anode. To reduce the operating voltage of electrolyzer, herein thermodynamically favorable glycerol oxidation reaction (GOR) is proposed to replace the OER. Moreover, vertical NiO flakes and NiMoNH nanopillars are developed to boost the reaction kinetics of anodic GOR and cathodic hydrogen evolution, respectively. Meanwhile, excluding the explosion risk of mixed H2/O2, a cheap organic membrane is used to replace the expensive anion exchange membrane in the electrolyzer. Impressively, the electrolyzer delivers a remarkable reduction of operation voltage by 280 mV, and exhibits good long-term stability. This work provides a new paradigm of hydrogen production with low cost and good feasibility.

For its important roles in biology, nitrogen monoxide (·NO) has become one of the most studied and fascinating molecules in chemistry. ·NO itself acts as a “noninnocent” or “redox active” ligand to transition metal ions to give metal–NO (M–NO) complexes. Because of this uncertainty due to redox chemistry, the real description of the electronic structure of the M–NO unit requires extensive spectroscopic and theoretical studies. We previously reported the Ni–NO complex with a hindered N3 type ligand [Ni(NO)(L3)] (L3− denotes hydrotris(3-tertiary butyl-5-isopropyl-1-pyrazolyl)borate anion), which contains a high-spin (hs) nickel(II) center and a coordinated 3NO−. This complex is very stable toward dioxygen due to steric protection of the nickel(II) center. Here, we report the dioxygen reactivity of a new Ni–NO complex, [Ni(NO)(I)(L1″)], with a less hindered N2 type bis(pyrazolyl)methane ligand, which creates a coordinatively unsaturated ligand environment about the nickel center. Here, L1″ denotes bis(3,5-diisopropyl-1-pyrazolyl)methane. This complex is also described as a hs-nickel(II) center with a bound 3NO−, based on spectroscopic and theoretical studies. Unexpectedly, the reaction of [Ni(NO)(I)(L1″)] with O2 yielded [Ni(κ2-O2N)(L1″)2](I3), with the oxidation of both 3NO− and the I− ion to yield NO2− and I3−. Both complexes were characterized by X-ray crystallography, IR, and UV–Vis spectroscopy and theoretical calculations.