Direct Electrolytic Splitting of Seawater: Opportunities and Challenges

Abstract

Hot, coastal, hyper-arid regions with intense solar irradiation and strong on- and off-shore wind patterns are ideal locations for the production of renewable electricity using wind turbines or photovoltaics. Given ample access to seawater and scarce freshwater resources, such regions make the direct and selective electrolytic splitting of seawater into molecular hydrogen and oxygen a potentially attractive technology. The key catalytic challenge consists of the competition between anodic chlorine chemistry and the oxygen evolution reaction (OER). This Perspective addresses some aspects related to direct seawater electrolyzers equipped with selective OER and hydrogen evolution reaction (HER) electrocatalysts. Starting from a historical background to the most recent achievements, it will provide insights into the current state and future perspectives of the topic. This Perspective also addresses prospects of the combination of direct seawater electrolysis with hydrogen fuel cell technology (reversible seawater electrolysis) and discusses its suitability as combined energy conversion–freshwater production technology.

Controlling Stability and Selectivity in the Competing Chlorine and Oxygen Evolution Reaction over Transition Metal Oxide Electrodes

“…I would like to point out that the presented strategy of exploring CER electrocatalysts with improved selectivity and stability can be equally employed to search for selective OER electrocatalysts, such as for electrocatalytic seawater splitting. [88,89] In this regard, the opposite free energy difference, i. e., ΔG(OCl)-ΔG(OOH), needs to be maximized to obtain a selective OER electrocatalyst based on transition metal oxides, where the CER is sufficiently suppressed. [13] However, in this case the stability issue might be problematic, since the OOH adsorbate limits the stability window of the transition metal oxide in acidic medium (cf.…”

Ultrasmall Co@Co(OH)2 Nanoclusters Embedded in N‐Enriched Mesoporous Carbon Networks as Efficient Electrocatalysts for Water Oxidation

“…Similarly,aset of peaks in the core-levels pectrumo fC1s reveals the presence of sp 2 -hybridized carbon C=C( 284.2 eV), C=NÀC( 285.7 eV), andC ÀO/C=O (288.2 eV; Figure 3c). The N1score-level spectrum was also deconvoluted into as et of four peaks corresponding to CÀN=C (398.3 eV;t riazine network), NÀ(C) 3 (399.6 eV;t ertiary N),C ÀNÀ H( 400.9 eV;p yrrolic-type N), andashake-up satellite peak (402.3 eV), as presented in Figure 3d. [31] The higher intensity of tertiaryNindicates the presence of ac onsiderable amount of heptazine units present in the whole structure.…”

“…It can decrease the deleterious consequences caused by the use of exhaustible fossil fuels on the environment around the globe . However, on a large scale, the realization of this potential technology is still limited by the need for high input potentials and the slow kinetics of the oxygen evolution reaction (OER), which mainly relies on the use of precious and earth‐scarce metals (Ir and Ru) as catalysts . Regarding this longstanding challenge, it is, therefore, highly desired to develop cost‐effective and competent electrode materials for efficient and long‐lasting OER reasonably close to the thermodynamic potential (1.23 V) or to even replace the benchmark precious metals.…”

“…[2] However,o nalarge scale, the realization of this potentialt echnology is still limited by the need for high input potentials and the slow kinetics of the oxygen evolution reaction (OER), which mainly relies on the use of preciousa nd earth-scarce metals (Ir and Ru)a sc atalysts. [1,3] Regarding this longstanding challenge, it is, therefore, highly desired to develop cost-effective and competent electrode materials for efficient and long-lasting OER reasonably close to the thermodynamic potential (1.23 V) or to even replace the benchmark precious metals. Over the past few decades, ag reat effort has been made to develop earth-abundant (Mn, Fe, Co, and Ni)metal-based electrocatalysts including oxides, chalcogenides,l ayeredd ouble hydroxides (LDH), and numeroush ybrid materials.…”

Porous PEI Coating for Copper Ion Storage and Its Controlled Electrochemical Release

“…However, direct electrolysis of seawater is still regarded as a most challenging endeavor in the future hydrogen economy. Beside intensive research on active and robust catalysts, the generation of chlorine gas during the oxidative splitting of seawater remains the most striking challenge . Herein, systematic electrochemical studies and surface analysis were performed to minimize the effect of the chlorine formation in side reactions.…”