Efficient Electrocatalytic Synthesis of Ammonia from Water and Air in a Membrane‐Free Cell: Confining the Iron Oxide Catalyst to the Cathode

Electrochemistry-Induced Improvements of Mechanical Strength, Self-Healing, and Interfacial Adhesion of Hydrogels

Hydrogels have demonstrated great potential in biomedical and engineering areas. To improve the physical performance, development of efficient physical/chemical protocols is essential. Herein, an electrochemistry functionalization strategy that is capable of enabling the functional improvements of hydrogel is reported. The electrochemistry functionalization is demonstrated on a hydrogel model of polyacrylamide (PAAm)@κ-carrageenan. The electrochemistry reaction generates metal ions (Fe³⁺ ) that migrate and coordinate with the sulfate groups of κ-carrageenan resulting in the prominent function improvements. In comparison with untreated PAAm@κ-carrageenan hydrogel, it can improve the mechanical strength by 7.37 times, and can increase the interfacial adhesion energy of the hydrogel on a glass surface from 0 to 1400 J m^-2 , stronger than the bonding strength of tendons (adhesion energy: ≈800 J m^-2 ). Two pieces of hydrogel strips integrate into an intact structure by the electrochemistry functionalization, where the healing efficiency reaches 100% in comparison to the untreated hydrogel. The most significant development is that it enables functional patterning on the hydrogel by the electrode assembly, which provides the hydrogel with modular sensitivity to external pressure. Therefore, it can be a general protocol for rapid generation of multifunctional hydrogels for biomedical and engineering developments.

Recent Advances in Solar Thermal Electrochemical Process (STEP) for Carbon Neutral Products and High Value Nanocarbons

Climate change represents one of the most important environmental issues of our time. Due to high levels of anthropogenic CO₂ emissions, atmospheric CO₂ has for the first time ever exceeded 415 ppm and has increased from 315 ppm in 1950. An annual increase in atmospheric CO₂ of ∼2 ppm is equal to a net increase of ∼15.6 billion tons of CO₂. The combustion of fossil fuels for electricity and transportation is still the main reason accounting for the CO₂ accumulation. On the top of that, fossil fuels are widely used in our modern industry for the productions of indispensable social staples. For instance, the millennia old thermal reduction of iron ore by charcoal or baked coal (3C + 2Fe₂O₃ → 4Fe + 3CO₂) continues as the main method for the production of iron. The artificial fertilizer ammonia boosts the global population and is mainly produced from the Haber-Bosch process, in which hydrogen is generated via steam reforming of methane (CH₄ + 2H₂O → 4H₂ + CO₂). Sequestration and diminution of CO₂ require the development of a portfolio of technologies on (1) efficient and long-term harvesting of renewable energy, that is, solar, not only for electricity but also directly as the energy force in vital chemical processes, wherever possible, (2) carbon-neutral processes to replace current industrial processes that emit vast amounts of CO₂, such as iron and ammonia production, and (3) new, low-cost technologies for CO₂ capture and conversion with particular interests in the exploration of CO₂ as the feedstock for fuels or other valuable chemicals and materials. To this end, we conducted some studies on the sustainable synthesis of ammonia and iron with net-zero CO₂ emissions and large-scale CO₂ capture and conversion into fuels and high value nanocarbon products via electrolysis in molten salt(s) with the introduction of the Solar Thermal Electrochemical Process (STEP). In STEP, solar UV-visible energy is focused on a photovoltaic device that generates the electricity to drive the electrolysis, while concurrently the solar thermal energy is focused on a second system to generate heat for the electrolysis cell. The utilization of the full spectrum of sunlight in STEP results in a higher solar energy efficiency than other solar conversion processes. STEP has been applied to conduct (1) CO₂-free ammonia synthesis from nitrogen and water with the aid of nano-Fe₂O₃ in a molten hydroxide electrolyte, (2) CO₂-free production of iron via electrochemical reduction of iron ore in molten carbonate, (3) CO₂ capture and conversion into nanostructured carbon products as well as fuels in molten or mixed molten electrolytes, and (4) organic electrosynthesis of benzoic acid from benzene without overoxidizing into CO₂. In this Account, we highlight some recent achievements in these topics and propose that using STEP is a highly efficient strategy for saving energy and, consequently, the environment. STEP is an ideal tool that can theoretically be applied to all endothermic reactions.