A new type of air-breathing photo-microfluidic fuel cell based on ZnO/Au using human blood as energy source

https://doi.org/10.1016/j.ijhydene.2019.10.003Get rights and content

Highlights

  • A new type of air-breathing photo-microfluidic fuel cell is presented.

  • ZnO/Au composite is used as a photo-anode.

  • An air-exposed Pt/C is employed as a cathode.

  • The micro-device is operated using human blood as a glucose source.

  • Visible light irradiated on the device increase the power density.

Abstract

The purpose of this work was the evaluation of a microfluidic fuel cell (μFC), in which human blood glucose was photo/electrochemically oxidized. In this regard, ZnO/Au composites with different Au content (1, 2 and 3%) were synthesized, as well as physicochemical and electrochemically characterized. In order to know if these ZnO/Au composites would serve as photo-electrocatalysts in a μFC, their photo- and electrochemical activities were analyzed. In this sense, the optical band gap of composites was determined as 3.15 eV, showing the typical surface plasmon resonance between 530 and 550 nm, while the electrocatalytic activity of ZnO/Au composites was evaluated in terms of the 5 mM glucose, showing that the minimum negative potential shift of the glucose oxidation peak corresponds to the composite with 3% of Au content. A μFC was fabricated using ZnO/Au 3% as photo-anode under visible-light, Pt/C as air-breathing cathode, and human blood and air coming from environment as fuel and oxidant, respectively. It was observed that μFC presented a 1.5-fold more power density under visible-light than in the darkness. This work represents an advantage in the use of photo-electrocatalyst materials towards the development of a new type of air-breathing photo-microfluidic fuel cells employing physiological fluids opening the possibility to be used as a power source in non-implantable medical devices.

Introduction

In recent years, applications of fuel cells have been intensified in the medical field either as implantable or non-implantable medical devices [1]. In the last application, the development of microfluidic fuel cells (μFC's) have been recognized as promising candidates for power supply [2,3]. Among the advantages of μFC's are: the elimination of membranes, the use of liquid fuels and oxidants [4], the operation with a single fuel fluid and the adaptation to breathe air from the environment [[5], [6], [7]]. In this sense, in a non-implantable medical device, a liquid sample employed for analysis, i.e. sweat [8], urine [9], or human blood [10], can also be used as fuel due to its content of lactic acid, urea and glucose, respectively. Therefore, the use of blood in the μFC's has been increased because many non-implantable medical devices use it in order to obtain medical diagnostic [[11], [12], [13]]. The evaluation of a glucose-μFC could be divided into three categories, i.e. ideal condition, near physiological condition and real condition. In a real condition, the sample of human serum and human blood are the source of glucose to be oxidized.

The search for catalytic materials that oxidize the glucose available in the human serum or human blood employed in μFC's devices has been mainly addressed towards the use of enzymes such as glucose oxidase and glucose dehydrogenase [2,3]. Nevertheless, the relatively short duration of the enzyme activity makes necessary to consider the use of precious metals that allow long-term stable performance and high power of the μFC's. Precious metals like Au supported on vulcan carbon or multi-walled carbon nanotubes have drawn attention for glucose oxidation. Gold, in the macroscale, is practically inert, however, when is synthesized as nanoparticles (usually < 10 nm), its reactivity strongly changes, having a considerable ability to catalyze oxidation reactions like glucose oxidation [14,15].

A tendency towards the use of materials that increase the power generated from the μFC's has been of great interest [16,17]. In this respect, the use of photoactive materials as support such as ZnO has been increased and [16], due to its low cost, easy of synthesis, relatively low optical band gap, high mobility of conduction electrons and its environmental stability [[18], [19], [20], [21]]. Besides, ZnO has shown its capacity as support and improves its performance when combining with Au- nanoparticles, despite this, ZnO/Au has not been used in μFC's [22,23]. Specifically, ZnO/Au material has been widely reported for glucose detection in microfluidic sensors and direct glucose fuel cells [[24], [25], [26]].

In the present work, we synthesized ZnO microparticles with six-blade impeller morphology and coated with different Au nanoparticles percentages (1, 2 and 3%) and in order to know if these ZnO/Au composites would serve as an anode for glucose photo/electro-oxidation in a μFC, their photo- and electrochemical activities were analyzed. Starting from the above, the objective of the following research was the fabrication of a μFC in a real application when human blood was used as fuel and air coming from environment as oxidant. The novelty of this work is the use of photo-catalysts materials in microdevices for power generation, which has not been widely studied, thus a new concept of a photo-microfluidic fuel cell was created. Also, in real applications, these photo-microfluidic fuel cells, based on the studied materials, could be an alternative to power-up non-implantable medical devices.

Section snippets

Reagents

ZnCl2 (>97%), NaOH (>97%) and SDS (>99%) were acquired from Jalmek (Mexico). Chloroauric acid (HAuCl4), hydrazine (N2H4) both with purities > 98% and glucose (reagent grade) were purchased from Sigma-Aldrich. KOH (98%) and isopropyl alcohol (98%) were purchased from J.T. Baker. Distilled grade water was used in the synthesis and purification.

Synthesis of ZnO and ZnO/Au nanoparticles

ZnO microparticles with six-blade impeller and cabbage-like morphologies were synthesized as reported elsewhere [20] and is briefly described: 8.2 g of

Morphology and optical properties

Fig. 2 shows the SEM images of the ZnO and ZnO/Au composites. It can be observed from Fig. 2a that ZnO microparticles consisted of agglomerates resembling morphologies of six blade impeller- and cabbage-like which are constructed of micrometric bi-dimensional sheets with sizes between 1 and 2 μm. Also, the Au nanoparticles are present onto the ZnO crystals as brilliant small dots (Fig. 2b and d) of sizes between 6 and 50 nm with average diameter of 40 nm. Table 1 shows the elemental

Conclusions

ZnO/Au composites were synthesized through an easy process with different Au content. The optical band gap of ZnO and its composites was 3.15 eV independent of the Au concentration, showing the typical surface plasmon resonance between 530 and 550 nm, which decreased as the Au content increased, due to the average particle size and particle size distributions of Au. The ZnO/Au composites were tested in the glucose electro-oxidation, where the minimum negative potential shift of the glucose

Acknowledgements

Author V.M.O.M acknowledges to National Council of Science and Technology (CONACYT), Mexico the financial support through grant #2017-INFR-280299. The authors A. Dector and J. M. Olivares-Ramírez gratefully acknowledge CONACYT for Cátedra CONACYT project 513.

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