Synthesis method of nickel-doped iron disulfide nanowire array structure on titanium sheet substrate
Technical Field
The invention relates to a method for synthesizing a doped transition metal sulfide, in particular to a method for synthesizing a nickel-doped iron disulfide nanowire array structure on a titanium sheet substrate.
Background
At present, with the development of society, the demand of various industries on energy is continuously increased, so that the design and development of high-performance, low-cost and high-efficiency nano energy materials become the direction of major attention of scientists. Especially in the field of electrocatalysis and electrochemical energy storage, the performance limitation of nanoelectrode materials is a problem for solution. Elemental sulfur in metal sulfide, outermost electron thereofHas a structure of 3S23P4The empty 3d orbit is close to the energy levels of the 3s and 3p orbitals, so that the d orbit has various bonding modes under certain conditions, the structure of the metal sulfide has diversity, abundant properties are shown, and the application range is wide. For example, cobalt disulfide, iron disulfide, nickel disulfide and the like can be applied to the fields of hydrogen production by electrolyzing water, oxygen production by electrolyzing water, super capacitors and lithium ion batteries. In order to further improve the electrochemical performance of the metal sulfide, more and more types of materials are invented, such as multiphase composite materials, alloy materials, doped materials and the like. The doping of the impurity element is a research hotspot due to the advantages of simple operation, wide selectivity and obvious performance improvement. If the nickel element is doped in the cobalt disulfide nano material or the molybdenum disulfide is doped with selenium, the electrocatalytic hydrogen production performance is obviously improved.
The pyrite type iron disulfide in the metal sulfide belongs to a cubic crystal system, has rich earth surface reserves, low cost and a forbidden band width of 0.95eV, and is a semiconductor material with wider application. The nano-level iron disulfide can be used as a potential electrode material and is generally applied to the fields of photoelectrocatalysis, electrochemical energy storage and the like. At present, work reports exist that cobalt ions are doped in an iron disulfide material and are compounded with a carbon nano tube, and the hydrogen production performance of the electrolyzed water is obviously improved compared with that of a pure-phase iron disulfide and carbon nano tube composite material. Therefore, the doping of the heteroatom plays a great contribution to the improvement of the hydrogen production of the iron disulfide material, and meanwhile, the performance of the iron disulfide material in the aspect of energy storage is expected to be improved, so that the method has certain research significance. Meanwhile, the nano material assembled on the conductive substrate can be directly used as an energy device to construct a high-efficiency electrochemical energy device, and has the advantages of simple and convenient operation, large active area, easy charge transmission and the like. However, the current doped metal sulfide has a certain limitation in application due to the complicated preparation method, poor conductivity and poor hydrogen production stability in an acid electrolyte. Based on the existing problems, a synthesis method of a nickel-doped iron disulfide nanowire array structure on a titanium sheet substrate is developed,the preparation steps are simple and easy to operate, the product has uniform appearance, good repeatability and stable structure, and the doping of nickel ensures that the material is 0.5M H2SO4The electrolyte shows hydrogen production catalytic activity and long-acting stability which are obviously superior to those of a pure iron disulfide nanowire array, and is expected to be widely applied to the fields of energy storage, photocatalysis, full electrolysis of water and the like.
Disclosure of Invention
The invention aims to overcome the limitation of the iron disulfide material in the aspect of electrochemical performance, and develops a method for synthesizing a nickel-doped iron disulfide nanowire array structure on a titanium sheet substrate.
The purpose of the invention can be realized by the following technical scheme:
the method for synthesizing the nickel-doped iron disulfide nanowire array structure on the titanium sheet substrate comprises the following steps:
(1) synthesizing a nickel-doped ferric oxide hydroxide nanowire array grown in situ on a titanium sheet substrate: dissolving ferric salt, nickel salt, sodium sulfate and urea in deionized water to obtain a reaction solution, putting a clean bare titanium sheet subjected to ultrasonic treatment, then placing the bare titanium sheet at a high temperature for reaction, taking out the titanium sheet after the reaction is finished, sequentially washing the titanium sheet with ethanol and deionized water, and drying the titanium sheet at 80 ℃ to obtain a nickel-doped ferric oxide hydroxide nanowire array (Ni-FeOOH/Ti) growing in situ;
(2) synthesizing a nickel-doped iron disulfide nanowire array structure on a titanium sheet substrate: and (2) placing the nickel-doped ferric oxide hydroxide nanowire array prepared in the step (1) in a tubular furnace, weighing sufficient sulfur powder and placing the sulfur powder in an air source port of the tubular furnace, repeatedly flushing argon for the tubular furnace to exhaust air, performing high-temperature gas-phase vulcanization under the protection of argon atmosphere at a certain flow rate, after the reaction is finished, naturally cooling a reaction device to room temperature, taking out the nickel-doped ferric disulfide nanowire array assembled on the titanium sheet substrate, sequentially cleaning the nickel-doped ferric oxide hydroxide nanowire array with ethanol and deionized water, and drying the nickel-doped ferric oxide hydroxide nanowire array at 80 ℃ to obtain the nickel-doped ferric disulfide nanowire array structure.
The ferric salt in the step (1) is ferric chloride hexahydrate, the nickel salt is nickel dichloride hexahydrate, and the sodium sulfate is anhydrous sodium sulfate. The reaction solution contains 20-30 mM of iron salt, 0-30 mM but not 0mM of nickel salt, 40-60 mM of sodium sulfate, and 0-50 mM but not 0mM of urea. The high-temperature reaction temperature is 110-130 ℃, and the reaction time is 6-12 h.
The ratio of the sulfur powder added in the step (2) to the nickel-doped ferric oxide hydroxide nanowire array is 1-2 g/1-2 cm2. The reaction temperature of the high-temperature gas phase vulcanization is 350-450 ℃, and the reaction time is 1-3 h. The argon flow rate was 25 sccm.
The prepared nickel-doped iron disulfide nanowire array is uniformly and firmly distributed on the surface of a titanium sheet, the average length of the nanowire is 200-250 nm, and the average diameter of the nanowire is 30-50 nm.
In the preparation process parameters, the proportion of the raw materials for synthesizing the precursor Ni-FeOOH nanowire, and the temperature and time of the gas-phase vulcanization reaction have decisive influence on the appearance, the structural stability and the product size of the final product. The raw material proportion has a decisive effect on the shape of the Ni-FeOOH nanowire and the structural stability assembled on the titanium sheet substrate, if the proportion exceeds a proper range, the shape of the material can be changed to a certain extent, and the structural stability of in-situ growth on the substrate can be correspondingly deteriorated; temperature and time of gas phase sulfidation reaction, Ni-FeS as final product2The performance and structural stability of the nanowires can be affected, and the product is insufficiently vulcanized and impure in phase due to too low temperature and too short time, so that the performance of the nanowires can be possibly deteriorated, and the product is deteriorated in structural stability due to too high temperature and the performance of the nanowires can also be affected.
The reaction system of the invention does not depend on accurate pH value, the product is uniformly distributed on the surface of the substrate, the structure is stable, the titanium sheet carrying the product is simply soaked and cleaned, and the gas phase reaction is simple, the by-products are few, and the success rate is high. Meanwhile, the material is directly assembled on the surface of the titanium sheet substrate, and can be directly used as a working electrode during lithium battery packaging and electro-catalysis test without the assistance of an adhesive and a series of complicated electrode preparation processes such as material mixing, film coating and the like, so that the reduction of conductivity is avoided, and the titanium sheet electrode has the advantages of simplicity and convenience in operation, large active area and the like.
Compared with the prior art, the nickel-doped iron disulfide nanowire array on the titanium sheet substrate synthesized by the method has the advantages of uniform appearance, uniform dispersion, capability of being densely and firmly distributed on the surface of the titanium sheet substrate, good repeatability and simple and easy synthesis method. The nickel doping is expected to further improve the performance of the iron disulfide nanowire array in the aspects of electrocatalytic hydrogen production and lithium ion batteries, and has good application prospects.
Drawings
In FIG. 1, a and b are scanning electron micrographs of FeOOH nanowire arrays and Ni-FeOOH nanowire arrays grown in situ on the titanium sheet substrates prepared in examples 1 and 2, respectively;
in FIG. 2, a and b are FeS assembled on the titanium sheet substrate prepared in examples 3 and 4 respectively2Scanning electron micrographs of nanowire arrays and Ni-FeS2 nanowire arrays;
FIG. 3 shows Ni-FeS assembled on the titanium sheet substrate prepared in example 42An X-ray diffraction pattern of the nanowire array;
FIG. 4 shows FeS assembled on the titanium plate substrate obtained in example 62And Ni-FeS2Linear volt-ampere hydrogen production curves of the nanowire array and the bare titanium sheet;
FIG. 5 shows Ni-FeS assembled on the titanium sheet substrate obtained in example 62Nanowire arrays (FIG. 5a) and FeS2Hydrogen production cycle stability test pattern of nanowire array (fig. 5 b);
FIG. 6 shows FeS assembled on the titanium plate substrate obtained in example 62And Ni-FeS2Electrochemical impedance spectrum of the nanowire array.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that variations and modifications can be made by persons skilled in the art without departing from the spirit of the invention. All falling within the scope of the present invention.
Example 1
Synthesis of FeOOH nanowire array grown in situ on titanium sheet substrate
Dissolving ferric trichloride hexahydrate and sodium sulfate in deionized water to obtain a reaction solution, wherein the concentration of ferric salt in the reaction solution is 25mM, and the concentration of sodium sulfate is 50mM, transferring the reaction solution into a reaction kettle, adding an ultrasonically treated clean bare titanium sheet into the reaction system, packaging the reaction system in the kettle, and placing the reaction system at 120 ℃ for reaction for 12 hours. And (3) taking out the titanium sheet after the reaction is finished, sequentially washing the titanium sheet by using ethanol and deionized water, and drying the titanium sheet at the temperature of 80 ℃ to obtain the in-situ grown FeOOH nanowire array. The obtained sample is shown in fig. 1(a), and a scanning electron microscope shows that FeOOH is a nanowire array structure uniformly grown on a titanium sheet substrate, and the diameter range of a single nanowire is about 50-80 nm.
Example 2
Synthesis of Ni-FeOOH nanowire array grown in situ on titanium sheet substrate
Dissolving ferric trichloride hexahydrate, nickel dichloride hexahydrate, sodium sulfate and urea in deionized water to obtain a reaction solution, wherein the concentration of ferric salt in the reaction solution is 25mM, the concentration of nickel salt is 25mM, the concentration of sodium sulfate is 50mM and the concentration of urea is 50mM, transferring the reaction solution into a reaction kettle, adding an ultrasonically treated clean bare titanium sheet into the reaction system, packaging the reaction system in the kettle, and placing the reaction system at 120 ℃ for reacting for 12 hours. And (3) taking out the titanium sheet after the reaction is finished, sequentially washing the titanium sheet by using ethanol and deionized water, and drying the titanium sheet at the temperature of 80 ℃ to obtain the in-situ grown Ni-FeOOH nanowire array. The obtained sample is shown in fig. 1(b), and a scanning electron microscope shows that Ni-FeOOH uniformly grows on a titanium sheet substrate and is in a nanowire array structure, and the diameter range of a single nanowire is about 40-60 nm.
Example 3
FeS on titanium sheet substrate2Synthesis of nanowire array structures
Dissolving ferric trichloride hexahydrate and sodium sulfate in deionized water to obtain a reaction solution, wherein the concentration of ferric salt in the reaction solution is 25mM, the concentration of sodium sulfate is 50mM, transferring the reaction solution into a reaction kettle, adding an ultrasonically treated clean bare titanium sheet into the reaction system, packaging the reaction system in the kettle, and placing the reaction system at 120 DEG CThe reaction was carried out for 12 hours. And (3) taking out the titanium sheet after the reaction is finished, sequentially washing the titanium sheet by using ethanol and deionized water, and drying the titanium sheet at the temperature of 80 ℃ to obtain the in-situ grown FeOOH nanowire array. Then shearing the prepared FeOOH/Ti to 2cm2Placing the titanium sheet substrate in a tubular furnace, weighing 2g of sulfur powder, placing the sulfur powder in an air source port of the tubular furnace, repeatedly flushing argon for the tubular furnace to exhaust air, vulcanizing at 450 ℃ for 3h under the protection of argon atmosphere with the flow rate of 25sccm, taking out the nickel-doped iron disulfide nanowire array assembled on the titanium sheet substrate after the reaction device is naturally cooled to room temperature, sequentially cleaning with ethanol and deionized water, drying at 80 ℃ and storing. The obtained sample is shown in FIG. 2(a), and the scanning electron microscope shows FeS2The diameter range of a single nanowire is about 40-70 nm for a nanowire array structure uniformly grown on a titanium sheet substrate.
Example 4
Ni-FeS on titanium sheet substrate2Synthesis of nanowire array structures
Dissolving ferric trichloride hexahydrate, nickel dichloride hexahydrate, sodium sulfate and urea in deionized water to obtain a reaction solution, wherein the concentration of ferric salt in the reaction solution is 25mM, the concentration of nickel salt is 25mM, the concentration of sodium sulfate is 50mM and the concentration of urea is 50mM, transferring the reaction solution into a reaction kettle, adding an ultrasonically treated clean bare titanium sheet into the reaction system, packaging the reaction system in the kettle, and placing the reaction system at 120 ℃ for reacting for 12 hours. And (3) taking out the titanium sheet after the reaction is finished, sequentially washing the titanium sheet by using ethanol and deionized water, and drying the titanium sheet at the temperature of 80 ℃ to obtain the in-situ grown Ni-FeOOH nanowire array. Then shearing the prepared Ni-FeOOH/Ti into 2cm2Placing the titanium sheet substrate in a tubular furnace, weighing 2g of sulfur powder, placing the sulfur powder in an air source port of the tubular furnace, repeatedly flushing argon for the tubular furnace to exhaust air, vulcanizing at 450 ℃ for 3h under the protection of argon atmosphere with the flow rate of 25sccm, taking out the nickel-doped iron disulfide nanowire array assembled on the titanium sheet substrate after the reaction device is naturally cooled to room temperature, sequentially cleaning with ethanol and deionized water, drying at 80 ℃ and storing. The obtained sample is shown in FIG. 2(b), and scanning electron microscopy shows Ni-FeS2The average length of the nano wire is 250nm, and the average diameter of the nano wire is 50 nm.
Example 5
Ni-FeS on titanium sheet substrate2Synthesis of nanowire array structures
Dissolving ferric trichloride hexahydrate, nickel dichloride hexahydrate, sodium sulfate and urea in deionized water to obtain a reaction solution, wherein the concentration of ferric salt in the reaction solution is 25mM, the concentration of nickel salt is 25mM, the concentration of sodium sulfate is 50mM and the concentration of urea is 50mM, transferring the reaction solution into a reaction kettle, adding an ultrasonically treated clean bare titanium sheet into the reaction system, packaging the reaction system in the kettle, and placing the reaction system at 110 ℃ for reacting for 6 hours. And (3) taking out the titanium sheet after the reaction is finished, sequentially washing the titanium sheet by using ethanol and deionized water, and drying the titanium sheet at the temperature of 80 ℃ to obtain the in-situ grown Ni-FeOOH nanowire array. Then shearing the prepared Ni-FeOOH/Ti to 1cm2Placing the titanium sheet substrate in a tubular furnace, weighing 1g of sulfur powder, placing the sulfur powder in an air source port of the tubular furnace, repeatedly flushing argon for the tubular furnace to exhaust air, vulcanizing at 350 ℃ for 1h under the protection of argon atmosphere with the flow rate of 25sccm, taking out the nickel-doped iron disulfide nanowire array assembled on the titanium sheet substrate after the reaction device is naturally cooled to room temperature, sequentially cleaning with ethanol and deionized water, drying at 80 ℃ and storing. The nanowires had an average length of 200nm and an average diameter of 30 nm.
Example 6
And (3) performing an electrolyzed water hydrogen production experiment on the nickel-doped iron disulfide nanowire array structure on the titanium sheet substrate.
An experimental instrument: CHI 660E electrochemical workstation.
Three-electrode system: saturated calomel electrode (reference electrode), graphite rod electrode (counter electrode), Ni-FeS2A working electrode of/Ti, FeS2a/Ti (working electrode), bare titanium sheet (working electrode).
Hydrogen-producing electrolyte: formulation 0.5M H2SO4The solution was tested for pH using an acidimeter.
The hydrogen production test method comprises the following steps: linear voltammetry, cyclic voltammetry, electrochemical impedance.
Construction of the working electrode:
(1) nickel doped iron disulfide nanowire array (Ni-FeS)2Nanowire arrays):
shearing a certain area of the titanium sheet substrate loaded with the catalyst material by using scissors, scraping the material of redundant parts, directly taking the titanium sheet substrate as a working electrode, and connecting the titanium sheet substrate with an electrochemical workstation through a platinum sheet electrode clamp;
(2) iron disulfide nanowire array (Ni-FeS)2Nanowire arrays):
shearing a certain area of the titanium sheet substrate loaded with the catalyst material by using scissors, scraping the material of redundant parts, directly taking the titanium sheet substrate as a working electrode, and connecting the titanium sheet substrate with an electrochemical workstation through a platinum sheet electrode clamp;
(3) comparing the working electrode:
the bare titanium sheet with a certain area is used as a working electrode for comparison, and the redundant part of the bare titanium sheet is stuck by an insulating adhesive tape so as to ensure that the hydrogen production area of the electrode is a fixed value.
The experimental steps are as follows:
(1) taking a proper amount of 0.5M H2SO4Putting the solution in an electrolytic cell, introducing nitrogen for about 20min, then building a three-electrode device, and testing Ni-FeS respectively2/Ti、FeS2Ti, linear voltammogram of bare titanium sheet (sweep rate 2 mV/s);
(2) taking a proper amount of 0.5M H2SO4Putting the solution in an electrolytic cell, introducing nitrogen for about 20min, then building a three-electrode device, and testing Ni-FeS respectively2/Ti、FeS2A first linear voltammogram of/Ti (sweep rate 2mV/s), and a linear voltammogram after 2000 rapid cyclic voltammograms (sweep rate 100mV/s) (sweep rate 2 mV/s);
(3) taking a proper amount of 0.5M H2SO4Putting the solution in an electrolytic cell, introducing nitrogen for about 20min, then building a three-electrode device, and testing Ni-FeS respectively2/Ti、FeS2The electrochemical impedance spectrogram of the/Ti has the test voltage of-440 mV and the frequency range of 0.1 Hz-105Hz, and a voltage amplitude of 5 mV.
Before each test, the electrolyte is saturated by introducing nitrogen for 20min, and removing the dissolved excessive oxygen. The linear voltammograms were all subjected to manual ohmic compensation. The test potential was corrected to a reversible hydrogen electrode by the following formula: e (RHE) ═ E (SCE) +0.242+0.059 pH.
And (4) analyzing results:
(1) FIG. 4 shows the Ni-FeS obtained by the test2/Ti、FeS2The linear voltammetry curves of the Ti and the bare titanium sheet are compared to find that the Ni-FeS is obtained by doping the nickel2the/Ti shows better performance than the pure phase FeS2The hydrogen production activity of Ti has lower hydrogen production overpotential and higher current density under the same voltage;
(2) FIG. 5 shows Ni-FeS2/Ti、FeS2Cycling stability of both/Ti, FIG. 5a shows Ni-FeS2the/Ti has higher repeatability and better catalytic stability compared with the first hydrogen production linear voltammetry curve after 2000 rapid cycle tests, and FIG. 5b shows that FeS2The Ti has poor catalytic stability, the activity of a hydrogen production curve after 2000 cycles is obviously attenuated relative to a first hydrogen production curve, and the overpotential of hydrogen production is obviously increased, so that the doping of the nickel is helpful to improve the FeS2The hydrogen production catalytic activity of the catalyst reduces hydrogen production overpotential and obviously improves the hydrogen production catalytic stability of the catalyst.
(3) FIG. 6 shows Ni-FeS2/Ti、FeS2The electrochemical impedance spectrum of the Ti/Ni can be found to be Ni-FeS under the same voltage2The conductive property of the/Ti is better.
The results of the performance tests further prove that the hydrogen production catalytic performance of the iron disulfide material is obviously improved by doping nickel, and the hydrogen production catalytic performance comprises the optimization of hydrogen production activity, the increase of conductivity and the enhancement of catalytic stability.
Example 7
The method for synthesizing the nickel-doped iron disulfide nanowire array structure on the titanium sheet substrate comprises the following steps:
(1) synthesizing a nickel-doped ferric oxide hydroxide nanowire array grown in situ on a titanium sheet substrate: dissolving ferric trichloride hexahydrate, nickel dichloride hexahydrate, sodium sulfate and urea in deionized water to obtain a reaction solution, wherein the concentration of ferric salt in the reaction solution is 30mM, the concentration of nickel salt is 30mM, the concentration of sodium sulfate is 60mM, and the concentration of urea is 50mM, transferring the reaction solution into a reaction kettle, putting a clean bare titanium sheet subjected to ultrasonic treatment into the reaction kettle, packaging the reaction kettle, reacting for 6 hours at 130 ℃, taking out the titanium sheet after the reaction is finished, sequentially washing the titanium sheet with ethanol and deionized water, and drying the titanium sheet at 80 ℃ to obtain a nickel-doped ferric hydroxide nanowire array (Ni-FeOOH/Ti) growing in situ;
(2) synthesizing a nickel-doped iron disulfide nanowire array structure on a titanium sheet substrate: placing the nickel-doped ferric oxide hydroxide nanowire array prepared in the step (1) in a tube furnace, weighing sufficient sulfur powder to be placed at an air source port of the tube furnace, wherein the proportional relation between the added sulfur powder and the nickel-doped ferric oxide hydroxide nanowire array is 2g/1cm2Repeatedly flushing argon for the tubular furnace to exhaust air, carrying out high-temperature gas phase vulcanization under the protection of argon atmosphere with the flow rate of 25sccm, wherein the reaction temperature is 450 ℃, the reaction time is 1h, after the reaction is finished, the reaction device is naturally cooled to the room temperature, taking out the nickel-doped iron disulfide nanowire array assembled on the titanium sheet substrate, sequentially cleaning the nickel-doped iron disulfide nanowire array with ethanol and deionized water, and drying the nickel-doped iron disulfide nanowire array at the temperature of 80 ℃, thereby obtaining the nickel-doped iron disulfide nanowire array structure, wherein the average length of the nanowires is 200nm, and the average diameter of the nanowires is 50 nm.
Example 8
The method for synthesizing the nickel-doped iron disulfide nanowire array structure on the titanium sheet substrate comprises the following steps:
(1) synthesizing a nickel-doped ferric oxide hydroxide nanowire array grown in situ on a titanium sheet substrate: dissolving ferric trichloride hexahydrate, nickel dichloride hexahydrate, sodium sulfate and urea in deionized water to obtain a reaction solution, wherein the concentration of ferric salt in the reaction solution is 20mM, the concentration of nickel salt is 0.1mM, the concentration of sodium sulfate is 40mM, and the concentration of urea is 0.1mM, transferring the reaction solution into a reaction kettle, putting clean bare titanium sheets subjected to ultrasonic treatment into the reaction kettle, packaging the reaction kettle, reacting at 110 ℃ for 12 hours, taking out the titanium sheets after the reaction is finished, sequentially washing the titanium sheets with ethanol and deionized water, and drying the titanium sheets at 80 ℃ to obtain a nickel-doped ferric oxide hydroxide nanowire array (Ni-FeOOH/Ti) growing in situ;
(2) synthesizing a nickel-doped iron disulfide nanowire array structure on a titanium sheet substrate: putting the nickel-doped ferric oxide hydroxide nanowire array prepared in the step (1) into a tube furnace, and weighing the footSulfur powder is put at the gas source port of the tube furnace, and the proportional relation between the added sulfur powder and the nickel-doped ferric oxide hydroxide nanowire array is 1g/2cm2Repeatedly flushing argon for the tubular furnace to exhaust air, carrying out high-temperature gas phase vulcanization under the protection of argon atmosphere with the flow rate of 25sccm, wherein the reaction temperature is 350 ℃, the reaction time is 3h, after the reaction is finished, the reaction device is naturally cooled to the room temperature, taking out the nickel-doped iron disulfide nanowire array assembled on the titanium sheet substrate, sequentially cleaning the nickel-doped iron disulfide nanowire array with ethanol and deionized water, and drying the nickel-doped iron disulfide nanowire array at the temperature of 80 ℃, thereby obtaining the nickel-doped iron disulfide nanowire array structure, wherein the average length of the nanowires is 250nm, and the average diameter of the nanowires is 30 nm.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes and modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention.