Electrocatalysis enables the industrial transition to sustainable production of chemicals using abundant precursors and electricity from renewable sources. De-centralized production of hydrogen peroxide (H2O2) from water and oxygen of air is highly desirable for daily life and industry. We report an effective electrochemical refinery (e-refinery) for H2O2 by means of electrocatalysis-controlled comproportionation reaction (2(H)O + O -> 2(HO)), feeding pure water and oxygen only. Mesoporous nickel (II) oxide (NiO) was used as electrocatalyst for oxygen evolution reaction (OER), producing oxygen at the anode. Conducting polymer poly(3,4-ethylenedioxythiophene): poly(styrene sulfonate) (PEDOT:PSS) drove the oxygen reduction reaction (ORR), forming H2O2 on the cathode. The reactions were evaluated in both half-cell and device configurations. The performance of the H2O2 e-refinery, assembled on anion-exchange solid electrolyte and fed with pure water, was limited by the unbalanced ionic transport. Optimization of the operation conditions allowed a conversion efficiency of 80%.

On-site electrosynthesis of hydrogen peroxide (H2O2) is a promising alternative technology to the conversional centralized anthraquinone oxidation process. Here, we report a platinum group metal (PGM)-free H2O2 electrogenerator with mesoporous Cr2O3 and NiCo2O4 used as electrocatalysts for oxygen reduction and evolution reactions (ORR and OER), respectively. The catalysts were synthesized via a hydrothermal synthesis route and had pore sizes of 3 and 7 nm and specific surface areas of 112 and 62 m(2) g(-1), respectively. Mesoporous Cr2O3 was evaluated in a half cell with 0.1 M KOH for electrocatalytic oxygen reduction, which shows 2.2 transferred electrons per oxygen and an in situ H2O2 yield of 70%. This enables the electrosynthesis of hydrogen peroxide in alkaline medium using Cr2O3 as a 2e-ORR-H2O2 electrocatalyst, with oxygen evolution as an auxiliary reaction on NiCo2O4. The effect of electrolyte flow on the H2O2 electrogenerator was investigated. It is observed that one-way feeding of the catholyte suppresses deterioration of the electrocatalyst and allows a faradic conversion up to similar to 90% with a production rate of similar to 0.36 [g (h<middle dot>g(cat))(-1)], operating within the cell voltage of 1.2 V. This work demonstrates both a viable method for electrosynthesis of H2O2 production using PGM-free electrocatalysts and the possibility to obtain a high faradic efficiency by mitigating the effect from catalyst degradation.

Electrocatalysis, the foundation of electrical to chemical energy transformation, enables the mitigation of the electrical energy losses during reactions and the control of selectivity of the process to certain chemical products. The slow rate and the multi-step complexity of oxygen-associated reactions, namely oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), motivate the use of platinum group metals (PGM) catalysts, which significantly increase the price of the technologies due to the cost and scarcity of PGM-based materials. This thesis aims to fundamentally understand the electrocatalytical aspects of oxygen-associated reactions and their relevance to sustainable technologies by development of cheap and abundant materials.

In this work, hydrothermal treatment routes are developed for synthesis of mesoporous MO_x (M = Cr, Fe, Co, Ni, Ce) and NiCo₂O₄ as water-processable oxygen electrocatalysts. Firstly, anionic surfactant templated mesoporous NiO shows the lowest voltage loss with the highest turnover frequency for OER in consequence of the most accessible active sites among of nanoporous nickel (II) oxide (Paper I). It is observed that nickel and cobalt oxides are efficient bifunctional oxygen electrocatalysts compared to other investigated metal oxides. This stems from the lower voltage loss and by the presence of surface adsorbed hydroxyl species. In situ quantification shows that hydrogen peroxide is either the terminal product or the intermediate for ORR on meso-Cr₂O₃ and on other electrocatalysts, respectively (Paper II). In Paper IV, mesoporous NiO and NiCo₂O₄ are synthesized by using a template-free hydrothermal route, and NiCo₂O₄ performs more efficient bifunctional oxygen catalysts compared to NiO. It is found that ORR on mesoporous NiO and NiCo₂O₄ follow (2+1)e- and 4e-ORR path, with hydroxyl radical and hydroxyl ion as terminal products, respectively.

Integrating the ORR and OER in electrochemical cells enables the study and development of energy conversion technologies. The bifunctional oxygen activity of meso-NiO is demonstrated in a PGM-free oxygen pump fed with air and water, resulting in a low faradic efficiency due to limited triple reaction points (Paper II). The performance of the oxygen pump has been significantly improved by exchanging the catalyst to mesoporous NiCo₂O₄ and the anolyte to concentrated KOH. The same setup is used for synthesis of the hydroxyl radical using mesoporous NiO. The hydroxyl radical is identified using degradation of rhodamine B, and a degradation rate of 0.034 min⁻¹ is obtained in Paper IV. Additionally, two effective 2e-ORR electrocatalysts of porous organic conducting polymer poly(3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) (Paper III) and mesoporous chromium (Paper V) have been studied for electrochemical refinery H₂O₂ by electrocatalysis-controlled comproportionation reaction (2𝐻₂𝑂 + 𝑂₂ → 2𝐻₂𝑂₂). It is observed that the hydrogen peroxide as terminal product of oxygen reduction shows ~70% Faradic efficiency on these two materials. The optimization of operation conditions on PEDOT: PSS-based hydrogen peroxide electrolyzer allows the conversion efficiency of 80% below 1V cell voltage. The optimized meso-Cr₂O₃-based hydrogen peroxide electrolyzer enables the conversion efficiency up to 90% that can be assigned to the suppressed of deterioration of catalyst.

To summarize, this thesis has developed mesoporous metal oxides use as PGM-free electrocatalysts for investigating oxygen-associated reactions in the alkaline condition. Furthermore, the work has explored the energy conversion applications using the functionality of the developed oxygen electrocatalysts.

Lignin, a byproduct from the pulp industry, is one of the redox active biopolymers being investigated as a component in the electrodes for sustainable energy storage applications. Due to its insulating nature, it needs to be combined with a conductor such as carbon or conducting polymer for efficient charge storage. Here, the lignin/carbon composite electrodes manufactured via mechanical milling (ball milling) are reported. The composite formation, correlation between performance and morphology is studied by comparison with manual mixing and jet milling. Superior charge storage capacity with approximate to 70% of the total contribution from the Faradaic process involving the redox functionality of lignin is observed in a mechanically milled composite. In comparison, manual mix shows only approximate to 30% from the lignin storage participation while the rest is due to the electric double layer at the carbon-electrolyte interface. The significant participation of lignin in the ball milled composite is attributed to the homogeneous, intimate mixing of the carbon and the lignin leading the electronic carrier transported in the carbon phase to reach most of the redox group of lignin. A maximum capacity of 49 mAh g(-1) is obtained at charge/discharge rate of 0.25 A g(-1) for the sample milled for 60 min.

Direct electrification of oxygen-associated reactionscontributesto large-scale electrical storage and the launch of the green hydrogeneconomy. The design of the involved catalysts can mitigate the electricalenergy losses and improve the control of the reaction products. Weevaluate the effect of the interface composition of electrocatalystson the efficiency and productivity of the oxygen reduction reaction(ORR) and oxygen evolution reaction (OER), both mechanistically andat device levels. The ORR and OER were benchmarked on mesoporous nickel-(II)oxide and nickel cobaltite (NiO and NiCo2O4,respectively) obtained by a facile template-free hydrothermal synthesis.Physicochemical characterization showed that both NiO and NiCo2O4 are mesoporous and have a cubic crystal structurewith abundant surface hydroxyl species. NiCo2O4 showed higher electrocatalytic activity in OER and selectivity towater as the terminal product of ORR. On the contrary, ORR over NiOyielded hydroxyl radicals as products of a Fenton-like reaction ofH(2)O(2). The product selectivity in ORR was usedto construct two electrolyzers for electrified purification of oxygenand generation of hydroxyl radicals.

Zn-ion batteries are one of the hot candidates for low-cost and sustainable secondary batteries. The hydrogen evolution and dendritic growth upon zinc deposition are todays challenges for that technology. One of the new strategies to cope with these issues is to use "water-in-salt" electrolyte (WISE), that is, super concentrated aqueous electrolytes, to broaden its electrochemical stability window (ESW), suppressing hydrogen evolution reaction (HER), and perturbing the dendritic growth. Herein, this work proposes to use "water-in-polymer salt" electrolyte (WIPSE) concept to mitigate the challenges with Zn ion batteries and bring this technology toward one of the cheapest, greenest, and most sustainable electrodes: Lignin-carbon (L-C) electrode. Potassium polyacrylate (PAAK) as WISE bears out as better electrolyte for L-C electrodes in terms of self-discharge, cyclic stability, and specific capacity compared to conventional electrolyte based on chemically cousin molecule potassium acetate. Zinc bis(trifluoromethanesulfonyl) imide (Zn(TFSI)(2)) added into WIPSE shows deposition and dissolution of Zn in Zn//Zn symmetric cell suggesting that Zn2+ are moving into the polyanionic network. Furthermore, the added bis (trifluor omethanesul fonyl) imide (TFSI-) metal salts trigger a approximate to 40% enhancement of the capacity of L-C electrode. These results show a new promising direction toward the development of cost-effective and sustainable Zn-lignin batteries.

Bifunctional electrocatalysts with both accelerated oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) enable high-power density electricity storage and decentralized extraction of pure oxygen from air for usage in health care. Herein, a hydrothermal synthesis employing the anionic surfactant sodium dodecyl sulfate as structure-directing agent is developed to fabricate a family of crystalline mesoporous metal oxides (meso-MO X , M = Cr, Fe, Co, Ni, Ce). The pore size and specific surface area depend on the metal used and they range from 3 to 6 nm and 60 to 200 m(2) g(-1), respectively. NiO and Co3O4 show a higher catalytic efficiency in alkaline media in comparison with the other oxides studied, and their activities are comparable with the values reported for platinum group metal (PGM)-based electrocatalysts. This stems from lower voltage losses and by the presence of specific hydroxide adsorbates on the surface. Both ORR and OER driven on Co3O4 show the unified rate-determining chemical step (|OO-|(center dot) (ads) + H2O <-> |OOH|(center dot) (ads) + OH-, where | X | ads are the species adsorbed on active sites). The bifunctional ORR/OER electrocatalysis obtained on mesoporous NiO is utilized for the first symmetrical PGM-free oxygen pump fed by air and water only.

Oxygen evolution reaction (OER) is critical for producing high purity hydrogen and oxygen via electrocatalytic water splitting. In this work, single crystalline, nanoporous nickel oxide (NiO) was prepared using a hydro thermal, soft-templated synthesis route followed by calcination at different temperatures. It is shown that the NiO crystals have a cubic lattice, and the pore size can be tuned from similar to 1 to similar to 70 nm by varying the calcination temperature, i.e. variation from micro to macroporosity. The NiOs catalytic performance as electrocatalysts was evaluated in OER, both thermodynamically and kinetically. Mesoporous NiO with calcination temperature of 400 degrees C had the lowest overpotential (335 mV) required @ 10 mA/cm(2) accompanied with the highest turnover frequency value and mass activity among of the obtained NiO electrocatalysts. The study shows that the electrocatalytic activity of nanoporous NiO outperforms that of commercial catalyst Ir/C (similar to 360 mV @ 10 mA/cm(2)). Microporous NiO possess the highest specific surface area and electrical double layer capacitance, while the nonporous NiO particles have the highest specific activity and BET activity of the catalysts. It is concluded that the minimization of voltage losses by the nanoscale enlargement of the electrocatalyst surface area shows the coherence between gas adsorption and electrocapacitive measurements. Conversely, the OER kinetics showed deterioration with surface area maximization due to the impediment of ionic transport inside the micropores. This work demonstrates the importance of morphology optimization to obtain an efficient OER electrocatalyst with low required overpotential and kinetic loss.