Bismuth iron molybdenum oxide solid solution: a novel and durable electrocatalyst for overall water splitting

Boosting the photoelectrochemical performance of BiVO4 by borate buffer activation: the role of trace iron impurities

BiVO4 is an attractive photoanode material for water oxidation, but requires surface treatment to improve the energy efficiency and stability. Herein, we investigate the role of borate buffer in activating the BiVO4 photoanode. We found that trace iron impurities in the borate buffer play a critical role in activating the photoanode. By optimizing the activation conditions, the photocurrent density attains 4.5 mA cm-2 at 1.23 VRHE without any cocatalysts, alongside a high ABPE value of 1.5% at 0.7 VRHE. Our study discloses the role of iron in the activation effect of borate buffer on the BiVO4 photoanode, which has implications for other catalytic systems.

Iron-impregnated cellulosic carbon as an effective electrocatalyst for seawater oxidation

The quest for cost effective but active electrocatalysts for water oxidation is at the forefront of research towards hydrogen economy. In this regard, bamboo as biomass derived N-doped cellulosic carbon has shown potential electrocatalytic performance towards water oxidation. The impregnation of optimum metallic Fe boosts the performance further, achieving an overpotential value of 238 mV at a benchmark current density of 10 mA cm-2. Owing to its promising OER performances in alkaline freshwater, the electrocatalyst was further explored in alkaline saline water and alkaline real seawater, exhibiting overpotentials of 272 mV and 280 mV, respectively, to reach 10 mA cm-2 current density. Most importantly, the protective graphitic multilayer surrounding the metallic Fe allowed the electrocatalyst to demonstrate excellent durability over 30 h even at a high current density in alkaline real seawater electrolyte.

Enthralling Anodic Protection by Molybdate on High-Entropy Alloy-Based Electrocatalyst for Sustainable Seawater Oxidation

Efficient and sustainable seawater electrolysis is still limited due to the interference of chloride corrosion at the anode. The designing of suitable electrocatalysts is one of the crucial ways to boost electrocatalytic activity. However, the approach may fall short as achieving high current density often occurs in chlorine evolution reaction (CER)-dominating potential regions. Thereby, apart from developing an OER-active high-entropy alloy-based electrocatalyst, the present study also offers a unique way to protect anode surface under high current density or potential by using MoO4 2- as an effective inhibitor during seawater oxidation. The wide variation of d-band center of high-entropy alloy-based electrocatalyst allows great oxygen evolution reaction (OER) proficiency exhibiting an overpotential of 230 mV at current density of 20 mA cm-2. Besides, the electrocatalyst demonstrates impressive stability over 500 h at high current density of 1 A cm-2 or at a high oxidation potential of 2.0 V versus RHE in the presence of a molybdate inhibitor. Theoretical and experimental studies reveal MoO4 2- electrostatically accumulated at anode surface due to higher adsorption ability, thereby creating a protective layer against chlorides without affecting OER.

Nickel Nanoparticles Protruding from Molybdenum Carbide Micropillars with Carbon Layer-Protected Biphasic 0D/1D Heterostructures for Efficient Water Splitting

It remains a tremendous challenge to achieve high-efficiency bifunctional electrocatalysts for both the hydrogen evolution reaction (HER) and the oxygen evolution reaction (OER) for hydrogen production by water splitting. Herein, a novel hybrid of 0D nickel nanoparticles dispersed on the one-dimensional (1D) molybdenum carbide micropillars embedded in the carbon layers (Ni/Mo2C@C) was successfully prepared on nickel foam by a facile pyrolysis strategy. During the synthesis process, the nickel nanoparticles and molybdenum carbide were simultaneously generated under H2 and C2H2 mixed atmospheres and conformally encapsulated in the carbon layers. Benefiting from the distinctive 0D/1D heterostructure and the synergistic effect of the biphasic Mo2C and Ni together with the protective effect of the carbon layer, the reduced activation energy barriers and fast catalytic reaction kinetics can be achieved, resulting in a small overpotential of 96 mV for the HER and 266 mV for the OER at the current density of 10 mA cm-2 together with excellent durability in 1.0 M KOH electrolyte. In addition, using the developed Ni/Mo2C@C as both the cathode and anode, the constructed electrolyzer exhibits a small voltage of 1.55 V for the overall water splitting. The novel designed Ni/Mo2C@C may give inspiration for the development of efficient bifunctional catalysts with low-cost transition metal elements for water splitting.

A comprehensive review on the electrochemical parameters and recent material development of electrochemical water splitting electrocatalysts

Electrochemical splitting of water is an appealing solution for energy storage and conversion to overcome the reliance on depleting fossil fuel reserves and prevent severe deterioration of the global climate. Though there are several fuel cells, hydrogen (H2) and oxygen (O2) fuel cells have zero carbon emissions, and water is the only by-product. Countless researchers worldwide are working on the fundamentals, i.e. the parameters affecting the electrocatalysis of water splitting and electrocatalysts that could improve the performance of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) and overall simplify the water electrolysis process. Noble metals like platinum for HER and ruthenium and iridium for OER were used earlier; however, being expensive, there are more feasible options than employing these metals for all commercialization. The review discusses the recent developments in metal and metalloid HER and OER electrocatalysts from the s, p and d block elements. The evaluation perspectives for electrocatalysts of electrochemical water splitting are also highlighted.

Transition Metal Non-Oxides as Electrocatalysts: Advantages and Challenges

The identification of hydrogen as green fuel in the near future has stirred global realization toward a sustainable outlook and thus boosted extensive research in the field of water electrolysis focusing on the hydrogen evolution reaction (HER), oxygen evolution reaction (OER), and oxygen reduction reaction (ORR). A huge class of compounds consisting of transition metal-based nitrides, carbides, chalcogenides, phosphides, and borides, which can be collectively termed transition metal non-oxides (TMNOs), has emerged recently as an efficient class of electrocatalysts in terms of performance and longevity when compared to transition metal oxides (TMOs). Moreover, the superiority of TMNOs over TMOs to effectively catalyze not only OERs but also HERs and ORRs renders bifunctionality and even trifunctionality in some cases and therefore can replace conventional noble metal electrocatalysts. In this review, the crystal structure and phases of different classes of nanostructured TMNOs are extensively discussed, focusing on recent advances in design strategies by various regulatory synthetic routes, and hence diversified properties of TMNOs are identified to serve as next-generation bi/trifunctional electrocatalysts. The challenges and future perspectives of materials in the field of energy conversion and storage aiding toward a better hydrogen economy are also discussed in this review.

Cobalt and iron phosphates with modulated compositions and phases as efficient electrocatalysts for alkaline seawater oxidation

An electrocatalyst which is suitable for use in both fresh water and real seawater electrolysis is very uncommon. In this work, we have developed a series of iron-tuned cobalt phosphates and cobalt-tuned iron phosphate solid solutions as electrocatalysts exhibiting excellent OER activities not only in freshwater but also in alkaline real seawater with a faradaic efficiency of 95%.

Cobalt chromium vanadium layered triple hydroxides as an efficient oxygen electrocatalyst for alkaline seawater splitting

Cobalt chromium vanadium layered triple hydroxides have been identified as a promising electrocatalyst for seawater splitting. The insertion of vanadium as a third metal into cobalt chromium layered double hydroxides not only adds extra cationic active sites but also facilitates electronic transition from Co(II) to V(V) boosting the OER activity and suppressing the CER.

Versatile Luminol/Dissolved Oxygen/Fe@Fe2O3 Nanowire Ternary Electrochemiluminescence System Combined with Highly Efficient Strand Displacement Amplification for Ultrasensitive microRNA Detection

Herein, a versatile ECL biosensor was fabricated for ultrasensitive detection of microRNA-21 (miRNA-21) from cancer cells based on a novel H₂O₂-free electrochemiluminescence (ECL) system (luminol/dissolved oxygen/Fe@Fe₂O₃ nanowires). Compared with the previously reported coreaction accelerator that needed a negative potential to produce reactive oxygen species (ROS), these newly discovered Fe@Fe₂O₃ nanowires could generate ROS in the detection solution immediately without the application of voltage, which narrowed down the detection potential range to avoid side reactions, favoring their practical application in biological systems. Especially, the Fe@Fe₂O₃ nanowires could produce H^• for activating dissolved oxygen into ROS to improve the ECL intensity dramatically, which initiates a novel pathway to promote the generation of ROS for the ECL system. In addition, an original strand displacement amplification coupled with strand displacement reaction (SDA-SDR) was developed to improve the conversion efficiency of the target for sensitive detection of miRNA-21. By virtue of the SDR, a quadruple quenching effect was achieved through each output DNA strand of SDA; hence, the nucleic acid signal amplification efficiency was effectively enhanced. As expected, on account of the superb activation performance of Fe@Fe₂O₃ nanowires and the outstanding amplification efficiency of the SDR-SDA strategy, the fabricated ECL biosensor realized ultrasensitive detection of miRNA-21 with a detection limit down to 52.5 aM. The established ECL sensing platform ushered a new route for H₂O₂-free detection and a promising biomarker assay method for clinical diagnosis.

Bifunctional Catalyst Derived from Sulfur-Doped VMoOx Nanolayer Shelled Co Nanosheets for Efficient Water Splitting

A novel sulfur-doped vanadium-molybdenum oxide nanolayer shelling over two-dimensional cobalt nanosheets (2D Co@S-VMoO_x NSs) was synthesized via a facile approach. The formation of such a unique 2D core@shell structure together with unusual sulfur doping effect increased the electrochemically active surface area and provided excellent electric conductivity, thereby boosting the activities for hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). As a result, only low overpotentials of 73 and 274 mV were required to achieve a current response of 10 mA cm^-2 toward HER and OER, respectively. Using the 2D Co@S-VMoO_x NSs on nickel foam as both cathode and anode electrode, the fabricated electrolyzer showed superior performance with a small cell voltage of 1.55 V at 10 mA cm^-2 and excellent stability. These results suggested that the 2D Co@S-VMoO_x NSs material might be a potential bifunctional catalyst for green hydrogen production via electrochemical water splitting.