Bifunctional sulfur-doped cobalt phosphide electrocatalyst outperforms all-noble-metal electrocatalysts in alkaline electrolyzer for overall water splitting

2020

Adv Materials Inter

their efficiencies, the catalysts employed are basically required to overcome the high energy barriers and sluggish kinetics of the electrochemical HER, OER, and ORR. [3] The benchmarking catalysts for ORR and HER are platinum (Pt)-based noble metal catalysts, whereas iridium (Ir) and ruthenium (Ru) oxides are highly active toward the OER. [4] Nevertheless, the high cost and scarcity of these precious metal-based catalysts have notably hindered their wide applications and commercialization. [5] Therefore, developing highly active, low cost, and sustained catalysts for these key electrocatalytic processes is paramount and apparently rewarding for the sustainable and large-scale implementation of clean energy devices. [6] To reduce, and hopefully to eliminate the usage of these precious metal-based catalysts, there have been intensive researches, in order to develop the practically and economically viable alternative electrocatalysts. [7] In this connection, phosphorus (P) is one of the most earth-abundant elements, thereby P-based materials have been considered being employed for electrocatalysis. [8] Indeed, P-based inorganic materials, especially the black phosphorus, metal phosphides, and metal phosphates, have attracted immense attention recently as a class of promising electrocatalysts, and presented intrinsic electrochemical activity and widely tunable properties. [9] Black phosphorus (BP) is a layer-structured semiconductor, in which individual atomic layers are stacked and held together by van der Waals interactions. [10,11] Until recently, BP stands out as a group of promising catalysts that have been investigated and shown to exhibit catalytic activities, owing to their unique puckered layer-structure, tunable band gap, and high carrier mobility. [12,13] As suggested by recent researches, 2D catalysts with reduced layer numbers or the thickness can present increased surface area and hence expose additional active sites, in comparison with their bulk counterparts. [14] To this end, phosphorene, as the building block for BP, possesses a monolayer (or a few layer) sheet structure, and has been explored for electrocatalysis and expected to promote the catalytic efficiency. [15,16] Nevertheless, because of the densely packed lone-pair p-electrons of phosphorus atoms, it would be hard for phosphorene to adsorb hydrogen, leading to the large hydrogen adsorption energy, and thus poor HER electrocatalytic Enormous progresses have been made in developing advanced energy conversion and storage technologies, which inevitably require high-performance electrocatalysts. Recently, phosphorus (P)-based materials have drawn tremendous attention as a class of promising electrocatalysts and presented intrinsic electrochemical activity and widely tunable property. In a timely response to the ongoing interests, issues faced in P-based inorganic materials, and the approaches to address them in relation to energy conversion reactions, including hydrogen evolution reaction, oxygen evolution reaction, and oxygen reduction reactio...

Section: Phosphidesmentioning

confidence: 99%

Phosphorus‐Based Electrocatalysts: Black Phosphorus, Metal Phosphides, and Phosphates

2020

Adv Materials Inter

“…[ 4 ] In addition, the most obtained electrocatalysts are not capable of possessing both excellent HER and OER performance in a same electrolyte due to incompatibility of activity over different pH ranges. [ 5 ] Therefore, constructing non‐noble metal bifunctional electrocatalysts with high performance and cost‐effectiveness has become a hot spot for efficient overall water splitting.…”

Section: Introductionmentioning

confidence: 99%

Interface Engineering of Hierarchical Branched Mo‐Doped Ni₃S₂/Ni_xP_y Hollow Heterostructure Nanorods for Efficient Overall Water Splitting

Luo

Advanced Energy Materials

et al. 2020

497

177

crisis and environmental issue. [1] Electrochemical water electrolysis offers a promising and effective strategy to produce high-quality H 2 without carbon emission. [2] However, the sluggish kinetics of hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) has been a huge challenge for water splitting, which has spurred researchers for exploiting high-efficiency electrocatalysts with reduced dynamic overpotentials. [3] AlthoughPt-based materials and Ru/Ir-based oxides are still known as the most efficient catalysts for HER and OER, they suffer from low abundance and high prices, leading to difficulties in the largescale commercial application. [4] In addition, the most obtained electrocatalysts are not capable of possessing both excellent HER and OER performance in a same electrolyte due to incompatibility of activity over different pH ranges. [5] Therefore, constructing non-noble metal bifunctional electrocatalysts with high performance and cost-effectiveness has become a hot spot for efficient overall water splitting.Recently, low-cost nickel chalcogenides, such as NiS, NiS 2 , and Ni 3 S 2 , have attracted enormous attention for electrolytic water splitting. [6] In particular, the Ni 3 S 2 electrocatalyst has been widely researched due to high conductivity and unique structure configuration, while the imprisoned HER/OER activity Rational design and construction of bifunctional electrocatalysts with excellent activity and durability is imperative for water splitting. Herein, a novel topdown strategy to realize a hierarchical branched Mo-doped sulfide/phosphide heterostructure (Mo-Ni 3 S 2 /Ni x P y hollow nanorods), by partially phosphating Mo-Ni 3 S 2 /NF flower clusters, is proposed. Benefitting from the optimized electronic structure configuration, hierarchical branched hollow nanorod structure, and abundant heterogeneous interfaces, the as-obtained multisite Mo-Ni 3 S 2 /Ni x P y /NF electrode has remarkable stability and bifunctional electrocatalytic activity in the hydrogen evolution reaction (HER)/oxygen evolution reaction (OER) in 1 m KOH solutions. It possesses an extremely low overpotential of 238 mV at the current density of 50 mA cm −2 for OER. Importantly, when assembled as anode and cathode simultaneously, it merely requires an ultralow cell voltage of 1.46 V to achieve the current density of 10 mA cm −2 , with excellent durability for over 72 h, outperforming most of the reported Ni-based bifunctional materials. Density functional theory results further confirm that the doped heterostructure can synergistically optimize Gibbs free energies of H and O-containing intermediates (OH*, O*, and OOH*) during HER and OER processes, thus accelerating the catalytic kinetics of electrochemical water splitting. This work demonstrates the importance of the rational combination of metal doping and interface engineering for advanced catalytic materials.The ORCID identification number(s) for the author(s) of this article can be found under https://doi.

“…Density functional theory (DFT) calculation further suggests that the enhanced catalytic activity for HER benefits from the synergistic modulation of the electronic properties and active components. In addition, Anjum et al indicated that S doping can significantly modify the electronic structures of CoP, thus improving its HER catalytic performance.…”

Section: Introductionmentioning

confidence: 99%

Hierarchically Porous W‐Doped CoP Nanoflake Arrays as Highly Efficient and Stable Electrocatalyst for pH‐Universal Hydrogen Evolution

Chen

et al. 2019

Small

132

It is still challenging to develop high‐efficiency and low‐cost non‐noble metal‐based electrocatalysts for hydrogen evolution reaction (HER) in pH‐universal electrolytes. Herein, hierarchically porous W‐doped CoP nanoflake arrays on carbon cloth (W‐CoP NAs/CC) are synthesized via facile liquid‐phase reactions and a subsequent phosphorization process. The W‐CoP NAs/CC hybrid can be directly employed as a binder‐free electrocatalyst and delivers superior HER performance in pH‐universal electrolytes. Especially, it delivers very low overpotentials of 89, 94, and 102 mV to reach a current density of 10 mA cm–2 in acidic, alkaline, and neutral electrolytes, respectively. Furthermore, it shows a nearly 100% Faradaic efficiency as well as superior long‐term stability with no decreasing up to 36 h in pH‐universal electrolytes. The outstanding electrocatalytic performance of W‐CoP NAs/CC can be mainly attributed to the porous W‐doped nanoflake arrays, which not only afford rich exposed active sites, but also accelerate the access of electrolytes and the diffusion of H2 bubbles, thus efficiently promoting the HER performance. This work provides a new horizon to rationally design and synthesize highly effective and stable non‐noble metal phosphide‐based pH‐universal electrocatalysts for HER.