Increasing demand for finding eco-friendly and everlasting energy sources is now totally depending on fuel cell technology. Though it is an eco-friendly way of producing energy for the urgent requirements, it needs to be improved to make it cheaper and more eco-friendly. Although there are several types of fuel cells, the hydrogen (H2) and oxygen (O2) fuel cell is the one with zero carbon emission and water as the only byproduct. However, supplying fuels in the purest form (at least the H2) is essential to ensure higher life cycles and less decay in cell efficiency. The current large-scale H2 production is largely dependent on steam reforming of fossil fuels, which generates CO2 along with H2 and the source of which is going to be depleted. As an alternate, electrolysis of water has been given greater attention than the steam reforming. The reasons are as follows: the very high purity of the H2 produced, the abundant source, no need for high-temperature, high-pressure reactors, and so on. In earlier days,...

Recent Trends and Perspectives in Electrochemical Water Splitting with an Emphasis on Sulfide, Selenide, and Phosphide Catalysts of Fe, Co, and Ni: A Review

The number of research reports published in recent years on electrochemical water splitting for hydrogen generation is higher than for many other fields of energy research. In fact, electrochemical water splitting, which is conventionally known as water electrolysis, has the potential to meet primary energy requirements in the near future when coal and hydrocarbons are completely consumed. Due to the sudden and exponentially increasing attention on this field, many researchers across the world, including our group, have been exerting immense efforts to improve the electrocatalytic properties of the materials that catalyze the oxygen evolution reaction (OER) at the anode and the hydrogen evolution reaction (HER) at the cathode, aided by the recent revolutionary discovery of nanomaterials. However, the pressure on the researchers to publish their findings rapidly has caused them to make many unnoticed and unintentional errors, which is mainly due to lack of clear insight on the activity parameters. In this perspective, we have discussed the use and validity of ten important parameters, namely overpotential at a defined current density, iR-corrected overpotential at a defined current density, Tafel slope, exchange current density (j0), mass activity, specific activity, faradaic efficiency (FE), turnover frequency (TOF), electrochemically active surface area (ECSA) and measurement of double layer capacitance (Cdl) for different electrocatalytic materials that are frequently employed in both OER and HER. Experimental results have also been provided in support of our discussions wherever required. Using our critical assessments of the activity parameters of water splitting electrocatalysis, researchers can ensure precision and correctness when presenting their data regarding the activity of an electrocatalyst.

Precision and correctness in the evaluation of electrocatalytic water splitting: revisiting activity parameters with a critical assessment

Exploring noble-metal-free electrocatalysts with high efficiency for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) holds promise for advancing the production of H2 fuel through water splitting. Herein, one-pot synthesis was introduced for MoS2–Ni3S2 heteronanorods supported by Ni foam (MoS2–Ni3S2 HNRs/NF), in which the Ni3S2 nanorods were hierarchically integrated with MoS2 nanosheets. The hierarchical MoS2–Ni3S2 heteronanorods allow not only the good exposure of highly active heterointerfaces but also the facilitated charge transport along Ni3S2 nanorods anchored on conducting nickel foam, accomplishing the promoted kinetics and activity for HER, OER, and overall water splitting. The optimal MoS2–Ni3S2 HNRs/NF presents low overpotentials (η10) of 98 and 249 mV to reach a current density of 10 mA cm–2 in 1.0 M KOH for HER and OER, respectively. Assembled as an electrolyzer for overall water splitting, such heteronanorods show a quite low cell voltage of 1.50 V at 10 mA...

MoS2–Ni3S2 Heteronanorods as Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting

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Heterostructures for Electrochemical Hydrogen Evolution Reaction: A Review

Developing bifunctional efficient and durable non-noble electrocatalysts for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is highly desirable and challenging for overall water splitting. Herein, Co–Mn carbonate hydroxide (CoMnCH) nanosheet arrays with controllable morphology and composition were developed on nickel foam (NF) as such a bifunctional electrocatalyst. It is discovered that Mn doping in CoCH can simultaneously modulate the nanosheet morphology to significantly increase the electrochemical active surface area for exposing more accessible active sites and tune the electronic structure of Co center to effectively boost its intrinsic activity. As a result, the optimized Co1Mn1CH/NF electrode exhibits unprecedented OER activity with an ultralow overpotential of 294 mV at 30 mA cm–2, compared with all reported metal carbonate hydroxides. Benefited from 3D open nanosheet array topographic structure with tight contact between nanosheets and NF, it is able to deliver a high and...

Electronic and Morphological Dual Modulation of Cobalt Carbonate Hydroxides by Mn Doping toward Highly Efficient and Stable Bifunctional Electrocatalysts for Overall Water Splitting

An Fe-doped CoP nanoarray behaves as a robust 3D monolithic multifunctional catalyst for electrolytic and hydrolytic hydrogen evolution with high activity Its two-electrode electrolyzer needs a cell voltage of only 160 V for 10 mA cm-2 water-splitting current It also catalyzes effectively NaBH4 hydrolysis with a low activation energy of ≈396 kJ mol-1 and a hydrogen generation rate of 606 L min-1 g-1 

Fe-Doped CoP Nanoarray: A Monolithic Multifunctional Catalyst for Highly Efficient Hydrogen Generation

Developing simple and cost-effective methods for the rapid synthesis of oxygen evolution reaction (OER) electrocatalysts from earth-abundant elements is a highly desired yet challenging task. Herein we report a two-step strategy based on the use of a room-temperature- and atmospheric-pressure-active iodine DBD plasma and an anion exchange reaction for the in situ generation of 3D Cu2S nanosheet arrays on Cu foam (Cu2S/CF). Owing to the advantages of this plasma-based approach, and the extremely rapid anion exchange reaction between the generated CuI and S2–, synthesis of the Cu2S/CF OER catalyst can be accomplished within 6 min. The porous 3D catalyst exhibited prominent electrocatalytic activity and persistent stability (>10 h) for OER with an overpotential of 336 mV to drive a geometrical current density of 20 mA cm–2 in 1.0 M KOH, comparable to the performance of a noble-metal IrO2/CF electrode.

Ultrarapid in Situ Synthesis of Cu2S Nanosheet Arrays on Copper Foam with Room-Temperature-Active Iodine Plasma for Efficient and Cost-Effective Oxygen Evolution

There is an urgent need for active and cost-effective catalysts for electrochemical hydrogen evolution reactions to solve global energy issues. In this study, we report the development of interconnected urchin-like cobalt phosphide microspheres film on Ti foil (u-CoP/Ti) as a monolithic hydrogen-evolving catalyst electrode with high activity and strong durability under acidic and alkaline conditions. It affords 10 mA cm−2 at overpotentials as low as 45 mV with the maintenance of its catalytic activity for at least 15 h in 0.5 M H2SO4, outperforming all reported CoP catalysts. When operated in 1.0 M KOH, u-CoP/Ti is also highly active and demands overpotential of 60 mV to drive 10 mA cm−2 with strong durability.

Interconnected urchin-like cobalt phosphide microspheres film for highly efficient electrochemical hydrogen evolution in both acidic and basic media

Due to their high abundance and potential to become alternatives to expensive platinum catalysts for large-scale hydrogen production through electrochemical water splitting, transition metal-based catalysts for the hydrogen evolution reaction (HER) have attracted intense interest over the past years Despite tremendous efforts, environmentally friendly and cost-effective synthesis of transition metal HER catalysts from scrap metal remains a challenge because of their large amounts of impurities Herein, a simple strategy combining room temperature photochemical vapor generation with low temperature deposition and phosphorization was developed to synthesize a 3D Ni2P catalyst from either pure nickel salt or bulk scrap nickel 3D NiO nanoparticles (NPs) were prepared for the first time via room temperature photochemical vapor generation and low temperature (160 °C) deposition Following complete phosphorization at low temperature, the 3D NiO NPs were converted to a highly active 3D Ni2P NPs HER catalyst Owing to its 3D nanostructure, the synthesized Ni2P NPs exhibited significant electrocatalytic performance and excellent stability in both acidic and alkaline media toward the HER with a low overpotential of 69 mV and 73 mV at 10 mA cm−2 Moreover, the chemical vapor generation and deposition processes could be precisely controlled and monitored with use of a miniaturized microplasma optical emission spectrometer

Cost-effective and environmentally friendly synthesis of 3D Ni2P from scrap nickel for highly efficient hydrogen evolution in both acidic and alkaline media

It is highly desirable to develop a simple, fast and straightforward method to boost the alkaline water oxidation of metal oxide catalysts. In this communication, we report our recent finding that the generation of amorphous Co-borate layer on Co3 O4 nanowire arrays supported on Ti mesh (Co3 O4 @Co-Bi NA/TM) leads to significantly boosted OER activity. The as-prepared Co3 O4 @Co-Bi NA/TM demands overpotential of 304 mV to drive a geometrical current density of 20 mA cm-2 in 1.0 M KOH, which is 109 mV less than that for Co3 O4 NA/TM, with its catalytic activity being preserved for at least 20 h. It suggests that the existence of amorphous Co-Bi layer promotes more CoOx (OH)y generation on Co3 O4 surface.

Liangbo He

Papers

Fe-Doped CoP Nanoarray: A Monolithic Multifunctional Catalyst for Highly Efficient Hydrogen Generation

Ultrarapid in Situ Synthesis of Cu2S Nanosheet Arrays on Copper Foam with Room-Temperature-Active Iodine Plasma for Efficient and Cost-Effective Oxygen Evolution

Interconnected urchin-like cobalt phosphide microspheres film for highly efficient electrochemical hydrogen evolution in both acidic and basic media

Cost-effective and environmentally friendly synthesis of 3D Ni2P from scrap nickel for highly efficient hydrogen evolution in both acidic and alkaline media

Co3O4 Nanowire Arrays toward Superior Water Oxidation Electrocatalysis in Alkaline Media by Surface Amorphization