Surface Roughening Strategy for Highly Efficient Bifunctional Electrocatalyst: Combination of Atomic Layer Deposition and Anion Exchange Reaction

Abstract

nontoxic, abundant, and durable catalysts with high activity toward the oxygen and hydrogen evolution reactions (OER and HER, respectively) are preferred. [3] Electrode material and architecture play critical roles in electrocatalytic water splitting. [4] Electrochemical reactions occur at the electrode-electrolyte interface; therefore, electrochemical processes are interfacedependent. Typically, only a fraction of the exposed sites, namely the surface active sites, participates in the electrochemical charge transfer process (Scheme 1a). The electrochemically active surface area (ECSA) generated by the electrical double layer formed at the electrode-electrolyte interface features numerous inactive surface sites that do not participate in electrochemical charge transfer (electronation-deelectronation). Building 3D architectures with large ECSAs is a common method for increasing active surface sites and accelerating electrochemical water splitting (Scheme 1b). In particular, coreshell architectures are highly desirable for good electrode performance because they combine the distinct properties of the core and shell materials used to build multifunctional electrodes. [5] For example, core-shell electrodes with NiCo 2 S 4 (NCS) cores and various shell structures have been evaluated for electrocatalytic water splitting. [6] However, coreshell architectures lengthen the electron transport pathways and increase electrode mass and interfacial resistance, hindering the efficient electrode utilization. The increase in total mass results in lower mass activity, although the estimated electrochemical performance of the core-shell structure is superior to that of the core structure as a function of the geometric area of the electrodes. Hence, developing innovative electrode nano-architectures to increase the N A with higher mass activity is an important task for developing commercial electrochemical energy conversion and storage devices. Nano-roughening the outer surfaces of nanostructures is an advanced method for increasing N A . It has similar ECSAs compared to conventional core-shell structures, but a greater proportion of active sites and massive mass activity. The ECSAs of the structures in Scheme 1b,d are the same; however, the ratio of active to inactive sites of the structure in Scheme 1d is higher than that of the structure in Scheme 1b. This can be achieved using several approaches, such as top-down physical etching, controlled Electrocatalytic water splitting, which is an interface-dominated process, can be significantly accelerated by increasing the number of front-line surface active sites (N A ) of the electrocatalyst. In this study, a unique method is used for increasing the N A by converting the smooth ultrathin atomic-layer-deposited nanoshells of the electrocatalysts into nano-roughened active shell layers using a controlled anion-exchange reaction (AER). The coarse thin nanoshells present abundant surface active sites, which are generated owing to the inherent unit-cell volume mismatch induced during th...

Engineering the surface anatomy of an industrially durable NiCo2S4/NiMo2S4/NiO bifunctional electrode for alkaline seawater electrolysis

“…The difference between the NCMO and sulfurized electrodes is due to the significant surface roughness created by the sulfurization process. 29 The incorporation of ALD-NiO increases the wettability of the prepared metal-sulfide electrodes as shown in Fig. 4(f).…”

“…The reduction of Ni 3+ to Ni 2+ is a single electron transfer reaction, therefore the number of electrons transferred ( N ) is equal to the N A . N = C / q , where q = 1.602 × 10 −19 C. 29 Chronopotentiometry measurements were conducted in a two-electrode setup at a constant current density with frequent replacement of the electrolyte. The amount of gas evolution during electrolysis was analyzed by gas chromatography (074-594-P1E Micro GC Fusion, INFICON).…”

“…[23][24][25][26][27][28] Recently, our group has achieved a subtle nano-roughened nanoshell architecture through a combination of atomic layer deposition (ALD) and anion exchange reaction with high electrochemical activity. 29 The structures consisting of a NiCo 2 S 4 thiospinel core covered with a NiS nanoshell with pronounced nanoroughness have achieved a durability of more than 10 days in an industrial high temperature seawater electrolyzer. Recently, Yu et al achieved the alkaline water splitting of seawater at 25 C temperature for more than 600 h of continuous operation.…”

High-Density NiMnFe Hydroxide Hierarchical Nano-arrays for Industrial-level Electro-chemical Oxygen Evolution Reaction

“…Managing the gas products on the microscopic electrode surfaces is actually of substantial importance to industrial level electrocatalytic process. 36 As we known, the adhesion behavior of gas bubbles can be tuned by the surface architecture construction, and nano-arrays structure with higher density is conducive to the desorption of bubbles. 37 We proposed that constructing the hierarchical structure can increase the density of nanoarray on the electrode surface.…”

Reconstruction of Ni–Co Phosphites Precatalyst into Metal Oxyhydroxides for Durable Full Water Electrolyzer Cell

“…Hydrogen production free from greenhouse gases is of great interest in the scenario of the speedy fading of nonrenewable fossil fuels and a gradual hike in energy demand. − Electrochemical water splitting is a leading approach to harvest high-quality hydrogen. − The process of water splitting is based on two half-reactions that occur at the anode and cathode, namely, oxygen evolution reaction (OER) and hydrogen evolution reaction (HER). − The key components in these two half-reactions are catalysts, which should possess high catalytic performance, possess robustness over the long run, overcome sluggish reactions, and possess economical efficiency in view of practicability . Although platinum and IrO 2 /RuO 2 are benchmark catalysts for their respective HER and OER activity, other impeding characteristics like compromising durability, scarcity, and high cost have been discouraging them toward real-time applicability. − Developing alternative and non-noble catalyst materials with lower overpotentials to drive high current density and remarkable stability as well as low cost is then highly desirable …”