Solar-driven, highly sustained splitting of seawater into hydrogen and oxygen fuels

Abstract

Electrolysis of water to generate hydrogen fuel is an attractive renewable energy storage technology. However, grid-scale freshwater electrolysis would put a heavy strain on vital water resources. Developing cheap electrocatalysts and electrodes that can sustain seawater splitting without chloride corrosion could address the water scarcity issue. Here we present a multilayer anode consisting of a nickel–iron hydroxide (NiFe) electrocatalyst layer uniformly coated on a nickel sulfide (NiSx) layer formed on porous Ni foam (NiFe/NiSx-Ni), affording superior catalytic activity and corrosion resistance in solar-driven alkaline seawater electrolysis operating at industrially required current densities (0.4 to 1 A/cm2) over 1,000 h. A continuous, highly oxygen evolution reaction-active NiFe electrocatalyst layer drawing anodic currents toward water oxidation and an in situ-generated polyatomic sulfate and carbonate-rich passivating layers formed in the anode are responsible for chloride repelling and superior corrosion resistance of the salty-water-splitting anode.

Designed Formation of Double‐Shelled Ni–Fe Layered‐Double‐Hydroxide Nanocages for Efficient Oxygen Evolution Reaction

“…The fast depletion of fossil fuels and the ever‐growing concerns over carbon dioxide emission advance the development of sustainable and environmentally friendly fuel sources. [ 1,2 ] Among variable alternatives, hydrogen has been considered as one ideal energy carrier because its combustion product is no more than water. [ 3–5 ] Electrochemical water splitting is one of the most promising strategies to create high‐purity hydrogen on a large scale in a green and economic way.…”

Reversible ternary nickel‐cobalt‐iron catalysts for intermittent water electrolysis

“…In this regards, multimetallic composites containing two or more metal components can exhibit enhanced electrochemical performances due to the synergistic metal-metal interactions, and also offer the flexibility to satisfy specific applications by adjusting the alloy compositions. Incorporation of iron (Fe) into nickel or cobalt, either as impurities or components, generates strong synergistic effects, resulting in significantly more active binary OER catalysts than either Ni or Co alone, [19][20][21][22][23][24][25][26][27][28][29] with some even outperforming the benchmark Ir-based catalysts. The combination of Ni and Co also leads to a substantial enhancement in the catalytic activity of HER.…”

Decoupling Oxygen and Chlorine Evolution Reactions in Seawater using Iridium‐based Electrocatalysts

“…[11] Oxygen generation from seawater electrolysis is attractive due to the abundance of seawater, which comprises 96.5 % of the Earth's total water reserves. [12] In seawater electrolysis, additional challenges arise with regards to the higher concentration of chloride anions (~0.5 M in seawater), [13] and practical implementation of this technology still faces many challenges, especially for the anodic reaction. [14] For example, in acidic conditions, the OER equilibrium potential vs. the standard hydrogen electrode (SHE) is 130 mV lower than that for the chlorine evolution reaction (CER; Equation 3), as described by the following two-electron pathway:…”

“…[18] Several works have sought to design materials that favor OER by incorporating manganese oxide coatings [19,20] or utilizing non-noble metal-based electrocatalysts. [13,14,17,21,22,23] This competition underscores the complex interplay between CER and OER. As such, we seek to understand this interplay electroanalytically by evaluating a series of iridium (Ir)-based electrocatalysts, as Ir is one of the most electroactive catalysts for OER in acidic electrolytes.…”

“…To further understand the competition between OER/CER, we evaluated the OER activity of the Ir2 electrocatalyst in synthetic seawater, a composition that mimics actual ocean condition in a practical electrolyte solution. Moststudies reported recently typically assess electrocatalytic OER/CER activity in either acidic or alkaline conditions, [13,17,18,19,20,21,22,23] or adding~0.5 wt% seawater in acidic electrolytes; [13] therefore, to follow the pioneering work from the chlor-alkali community, [16] we tested our electrodes in synthetic seawater to better depict the performance in a more relevant system. By transitioning towards a higher Na + and Cl À concentration system with a near-neutral pH of 7, the overpotential increased to 560 mV ( Figure 4b).…”