Water Splitting:From Electrode to Green Energy System

Hydrogen(H2)production is a latent feasibility of renewable clean energy.The industrial H2 production is obtained from reforming of natural gas,which consumes a large amount of nonrenewable energy and simultaneously produces greenhouse gas carbon dioxide.Electrochemical water splitting is a promising approach for the H2 production,which is sustainable and pollution-free.Therefore,developing efficient and economic technologies for electrochemical water splitting has been an important goal for researchers around the world.The utilization of green energy systems to reduce overall energy consumption is more important for H2 production.Harvesting and converting energy from the environment by different green energy systems for water splitting can efficiently decrease the external power consumption.A variety of green energy systems for efficient producing H2,such as two-electrode electrolysis of water,water splitting driven by photoelectrode devices,solar cells,thermoelectric devices,triboelectric nanogenerator,pyroelectric device or electrochemical water-gas shift device,have been developed recently.In this review,some notable progress made in the different green energy cells for water splitting is discussed in detail.We hoped this review can guide people to pay more attention to the development of green energy system to generate pollution-free H2 energy,which will realize the whole process of H2 production with low cost,pollution-free and energy sustainability conversion.

Chromium phosphide nanoparticles embedded in porous nitrogen-/phosphorus-doped carbon as efficient electrocatalysts for a nitrogen reduction reaction

The resource recovery of heavy metals from effluent has significant environmental implications and potential commercial value.Chromium phosphide nanoparticles embedded in a nitrogen-/phosphorus-doped porous carbon matrix(CrP/NPC)are synthesized via a consecutive Cr^(6+)leachate treatment and resource recovery process.Electrochemical testing shows that CrP/NPC shows excellent nitrogen reduction reaction(NRR)performance,which yields the highest NH_(3) production rate of 22.56μg h^(−1) mg^(−1)_(cat).and Faradaic efficiency(16.37%)at−0.5 V versus the reversible hydrogen electrode in a 0.05M Na_(2)SO_(4) aqueous solution,as well as robust catalytic stability.The isotopic experiments using ^(15)N^(2) as a nitrogen source confirm that the detected NH_(3) is derived from the NRR process.Finally,density functional theory(DFT)calculations show that the electron deficiency environment of the Cr site can significantly reduce the barrier of the NRR process and promote the formation of intermediate species.

Electrospinning-derived functional carbon-based materials for energy conversion and storage

The over-exploitation of fossil fuel energy has brought about serious environmental problems.It would be of great significance to construct efficient energy conversion and storage system to maximize utilize renewable energy,which contributes to reducing environmental hazards.For the past few years,in terms of electrocatalysis and energy storage,carbon fiber materials show great advantages due to its outstanding electrical conductivity,good flexibility and mechanical property.As a simple and low-cost technique,electrospinning can be employed to prepare various nanofibers.It is noted that the functional fiber materials with different special structure and composition can be obtained for energy conversion and storage by combining electrospinning with other post-processing.In this paper,the structural design,controllable synthesis and multifunctional applications of electrospinning-derived functional carbon-based materials(EFCMs)is reviewed.Firstly,we briefly introduce the history,basic principle and typical equipment of electrospinning.Then we discuss the strategies for preparing EFCMs with different structures and composition in detail.In addition,we show recently the application of advanced EFCMs in energy conversion and storage,such as nitrogen species reduction reaction,CO_(2) reduction reaction,oxygen reduction reaction,water-splitting,supercapacitors and ion batteries.In the end,we propose some perspectives on the future development direction of EFCMs.

Metal-encapsulated nitrogen-doped carbon nanotube arrays electrode for enhancing sulfion oxidation reaction and hydrogen evolution reaction by regulating of intermediate adsorption

For treatment of sulfion-containing wastewater,coupling the electrochemical sulfion oxidation reaction(SOR)with hydrogen evolution reaction(HER)can be an ideal way for sulfur and H_(2)resources recovery.Herein,we synthesize a metal-modified carbon nanotube arrays electrode(Co@N-CNTs/CC)for SOR and HER.This electrode has excellent performance for SOR and HER attributed to the unique array structure.It can achieve 99.36 mA/cm^(2)at 0.6 V for SOR,and 10 mA/cm^(2)at 0.067 V for HER.Density functional theory calculations verify that metal modification is able to regulate the electronic structure of carbon nanotube,which is able to optimize the adsorption of intermediates.Employed Co@N-CNTs/CC as bifunctional elec-trodes to establish a hybrid electrolytic cell can reduce about 67%of energy consumption compared with the traditional water splitting electrolytic cell.Finally,the hybrid electrolytic cell is used to treat actual sulfion-containing wastewater,achieving the sulfur yield of 30 mg h^(−1)cm^(−2)and the hydrogen production of 0.64 mL/min.

Single-atom catalyst application in distributed renewable energy conversion and storage

In recent years,owing to the depletion of fossil energy and the aggravation of environmental pollution,the conversion and storage of distributed renewable energy(such as solar energy,wind energy,and tidal energy)based on electrochemical technology have attracted extensive attention.Electrocatalytic processes with high efficiency and high selectivity play a key role in clean energy conversion and storage.With the nearly 100%atomic utilization rate and unique catalytic activity,single-atom catalysts(SACs)have been rapidly developed and widely used in the field of energy conversion and storage.In this review,we first introduce the characteristics of SACs.Then,we focus on the application of SACs in energy conversion,including water electrolysis reaction,nitrogen reduction reaction,nitrate reduction reaction,oxygen reduction reaction,and carbon dioxide reduction reaction.In terms of energy storage,we focus on supercapacitors and Li–S batteries.Further,we enumerate some of the methods for the synthesis of SACs in high metal loading or large scale.Finally,the main challenges and opportunities for this emerging field in the future are discussed and prospected.

A novel synthetic method of porous and nanoflower-like Al_(2)O_(3)/MoS_(2)catalyst for reduction of SO_(2)to elemental sulfur

MoS_(2)nanoflowers are favored for their potential in the production of elemental sulfur due to abundant surface area and good catalytic performance for reducing SO_(2).A novel synthetic strategy of porous Al_(2)O_(3)supported on the MoS_(2)with nanoflower structure was proposed.The effects of preparation concentration,calcination atmosphere,Al_(2)O_(3)contents on the growth of catalysts with nanoflower structure were systematically studied via X-ray diffraction(XRD),scanning electron microscopy(SEM),X-ray photoelectron spectroscopy(XPS),transmission electron microscopy(TEM),Fourier transform infrared(FTIR)spectroscopy,Brunauer–Emmett–Teller(BET).The surface area was increased to 295.502 m^(2)/g and the amount of Lewis acid on the surface of the Al_(2)O_(3)/MoS_(2)catalyst was increased by adjusting the ratio of Al/Mo.The porous and nanoflower structures of Al_(2)O_(3)/MoS_(2)catalysts promoted the sulfur selectivity without inhibiting the catalytic performance of MoS_(2).The conversion of SO_(2)and the selectivity of sulfur were 100%and 92%after 100 h life evaluation.

磷钼钒酸催化甲基丙烯醛氧化反应机制及过程研究

围绕甲基丙烯醛选择性氧化制甲基丙烯酸的反应过程,利用原位红外分析装置研究了甲基丙烯醛在磷钼钒酸催化剂上的原位吸附和反应过程,发现了甲基丙烯醛在杂多酸催化剂桥氧键吸附产生的中间结构,并提出了该催化过程的反应机理。进一步获得了不同温度下反应过程的中间状态,发现钒氧物种由一级结构迁移至二级结构能有效提高催化性能。优化了催化剂预还原温度,250℃下还原3 h后催化剂活性最高。

Enhanced electrocatalytic activity of Co@N-doped carbon nanotubes by ultrasmall defect-rich TiO2 nanoparticles for hydrogen evolution reaction

Despite being technically possible, splitting water to generate hydrogen is practically unfeasible, mainly because of the lack of sustainable and efficient earth-abundant catalysts for the hydrogen-evolution reaction （HER）. Herein, we report a durable and highly active electrochemical HER catalyst based on defect-rich TiO2 nanoparticles loaded on Co nanoparticles@N-doped carbon nanotubes （D-TiOdCo@NCT） synthesized by electrostatic spinning and a subsequent calcining process. The ultrasmall TiO2 nanoparticles are 1.5-2 nm in size and have a defect-rich structure of oxygen vacancies. D-TiO2/Co@NCT exhibits excellent HER catalytic activity in an acidic electrolyte （0.5 M H2SO4）, with a low onset potential of -57.5 mV （1 mA·cm^-2）, a small Tafel slope of 73.5 mV·dec^-1, and extraordinary long-term durability. X-ray photoelectron spectroscopy, electron paramagnetic resonance spectroscopy, and theoretical calculations confirm that the Ti3. defect-rich structure can effectively regulate the catalytic activity for electrochemical water splitting.

One-step synthesis of Fe-Ni hydroxide nanosheets derived from bimetallic foam for efficient electrocatalytic oxygen evolution and overall water splitting

The research of superior water oxidation electrodes is essential for the green energy in the form of hydrogen by way of electrolytic water splitting, and still remains challenging. Based upon dealloying foam, Fe-Ni hydroxide nanosheets network structure is designed on the surface of Fe-Ni alloy foam. The ratio of Ni/Fe elements was adjusted to realize the optimal catalytic activities for oxygen evolution reaction（OER） and hydrogen evolution reaction（HER）. The obtained electrode of Fe-Ni hydroxide nanosheets/Fe-Ni alloy foam-60% Fe（FN LDH/FNF-60, 60 is the percentage of Fe content） possess low overpotential of 261 mV to reach 10 mA/cm;, small Tafel slope（85.5 mV/dec）, and superior long-term stability（remaining 10 mA/cm;for over 14 h without attenuation） toward OER in 1.0 mol/L KOH.Moreover, an alkaline water electrolyzer is constructed with the FN LDH/FNF-60 as anode and Ni（OH）;/Fe-Ni alloy foam-25% Fe(Ni（OH）;/FNF-25) as cathode, which displays superior electrolytic performance（affording 10 mA/cm;at 1.62 V） and lasting durability.

Waste-yeast biomass as nitrogen/phosphorus sources and carbon template:Environment-friendly synthesis of N,P-Mo_(2)C nanoparticles on porous carbon matrix for efficient hydrogen evolution

Tailor-made advanced electrocatalysts with high active and stable for hydrogen evolution reaction(HER)play a key role in the development of hydrogen economy.Herein,a N,P-co-doped molybdenum carbide confined in porous carbon matrix(N,P-Mo_(2)C/NPC)with a hierarchical structure is prepared by a resources recovery process.The N,P-Mo_(2)C/NPC compound exhibits outstanding HER activity with a low overpotential of 84 mV to achieve 10 mA/cm^(2),and excellent stability in alkaline media.The electrochemical measurements confirm that the enhanced HER activity of N,P-Mo_(2)C/NPC is ascribe to the synergy of N,P-codoped and porous carbon matrix.Density functional theory calculations further reveal that the electron density of active sites on Mo_(2)C can be regulated by the N/P doping,leading to optimal H adsorption strength.In this work,the proof-of-concept resource utilization,a microorganism derived molybdenum carbide electrocatalyst for HER is fabricated,which may inaugurate a new way for designing electrocatalysts by the utilization of solid waste.

Ruthenium nanoclusters anchored on cobalt phosphide hollow microspheres by green phosphating process for full water splitting in acidic electrolyte

Transition metal phosphide(TMP) based electrocatalysts possessing special crystal and electronic structures attract broad attention in the field of electrocatalysis.Immense effort is made to optimize TMP catalysts aiming to satisfy the electrochemical catalysis performance.In this work,an environmentally friendly in situ green phosphating strategy and spatial limiting effect of the RuCo precursor is employed to fabricate the ruthenium nanoclusters anchored on cobalt phosphide hollow microspheres(Ru NCs/Co_(2)P HMs).The obtained Ru NCs/Co_(2)P HMs electrocatalysts exhibit high hydrogen evolution reaction(HER) activity at wide pH ranges,which require an overpotential of 77 mV to achieve the current density of 10 mA/cm^(2) in 0.5 mol/L H_(2)SO_(4) and 118 mV in 1.0 mol/L KOH.Besides,the multifunctional Ru NCs/Co_(2)P HMs exhibit good oxygen evolution reaction(OER) activity with an overpotential of 197 mV to reach the current density of 10 mA/cm^(2) in 0.5 mol/L H_(2)SO_(4),which is below that of the commercial RuO_(2) electrocatalyst(248 mV).A two-electrode electrolyzer is assembled as well,in acid electrolyte,it achieves a current density of 10 mA/cm^(2) at a voltage of 1.53 V,which is superior to that of the benchmark of precious metal-based electrolyzer(1.58 V).