Water-Formation-Energy-Driven Electrochemical Process Modulation

ConspectusWater formation through H⁺/OH^- recombination, traditionally viewed as an electrochemically inert, nonredox process, harbors untapped potential when re-examined through an electrochemical perspective. Recent progress highlights that this energy, close to 160000 trillion joules/year globally, often lost in industrial neutralization processes, can be electrochemically captured within a decoupled acid-alkali framework by utilizing a hydrogen redox, albeit without a net redox. This paradigm shift unlocks unique opportunities and possibilities for electrochemical process modulation, often driving thermodynamically uphill reactions spontaneously under ambient conditions, transcending the capabilities of conventional electrochemical energy devices. In this Account, we delineate recent conceptual breakthroughs and experimental progress that have advanced the mechanistic comprehension and functional implementation of water formation energy (WFE) processes as well as the thermodynamic and kinetic factors that dictate their efficiency. Critical to this innovation is the strategic use of hydrogen redox, which enabled the direct capturing of WFE as an electrical driving force, leading to a unique class of galvanic and electrolytic devices with multifunctional capabilities. Introducing a temperature gradient into this WFE system yields a galvanic-thermogalvanic hybrid device, utilizing entropy gain and enhancing the energy output of WFE-based devices. A galvanic desalination concept based on WFE demonstrates salt removal during electricity generation through an eventually nonredox process involving only gases and water species, avoiding contamination of the desalination pathway. The WFE approach facilitates spontaneous hydrogen fuel purification and decarbonization from complex impurity streams in a single step at room temperature and pressure. Additionally, the design of a spontaneous isotopic water formation cell by harvesting heavy water formation energy results in the unique generation of heavy hydrogen at the expense of light hydrogen. WFE enables ambient-condition reformation of hydrogen storage molecules, including hydrazine, aliphatic and aromatic alcohols, and biomass derivatives, marking a new era of green chemistry. Its integration into zinc batteries affords dual utilities: high-performance energy storage coupled to on-demand electro-organic synthesis, peroxide production, and clean hydrogen generation. In aqueous supercapacitors, WFE extends the voltage window to nearly 2 V, beyond thermodynamic constraints, thereby boosting the energy storage without compromising their power capabilities. Moreover, WFE underpins low-voltage electro-organic synthesis of valuable chemicals paired with hydrogen fuel synthesis, low-bias photoelectrochemical water splitting, and electricity-efficient electrolytic desalination, providing a versatile toolkit for modulating next-generation electrolytic processes. This Account underlines that WFE, once overlooked due to its nonredox nature, now stands as a rich, tunable, and scalable thermodynamic platform. Its strategic electrochemical capturing not only elevates the efficiency and sustainability of electrochemical systems, but also paves the way for a new paradigm in energy science, transforming what was once deemed an inert process into a cornerstone of the next-generation electrochemical technologies.