Biobat­ter­ies Catch Breath

People are increas­ingly tak­ing advant­age of devices sup­port­ing vari­ous func­tions of our bod­ies. Today they include car­di­ac pace­makers or hear­ing aids; tomor­row it will be con­tact lenses with auto­mat­ic­ally chan­ging focal length or com­puter-con­trolled dis­plays gen­er­at­ing images dir­ectly in the eye. None of these devices will work if not coupled to an effi­cient and long-last­ing power sup­ply source. The best solu­tion seems to be mini­atur­ised bio­fuel cells con­sum­ing sub­stances nat­ur­ally occur­ring in human body or in its dir­ect sur­round­ing. Research­ers from the Insti­tute of Phys­ic­al Chem­istry of the Pol­ish Academy of Sci­ences (IPC PAS) in Warsaw developed an effi­cient elec­trode for the use in con­struc­tion of bio­fuel cells or zinc-oxy­gen biobat­ter­ies. After install­a­tion in a cell, the new biocath­ode gen­er­ates a voltage, dur­ing many hours, that is high­er than that obtained in exist­ing power sources of sim­il­ar design. The most inter­est­ing is that the device is air-breath­ing: it works at full effi­ciency when it can take oxy­gen dir­ectly from the air. Com­mon bat­ter­ies and rechargeable bat­ter­ies are unsuit­able to power implants inside the human body as they use strong bases or acids. These agents can on no account get into the body. The bat­tery hous­ing must be there­fore abso­lutely tight. But in line with redu­cing the bat­tery size, it must be bet­ter isol­ated. In extreme cases, the weight of the hous­ing of a com­mon, mini­atur­ised bat­tery would be even a few dozen times great­er than the weight of the bat­tery’s act­ive com­pon­ents that gen­er­ate elec­tri­city. And here bio­fuel cells offer an essen­tial advant­age: they do not require hous­ing. To get elec­tri­city, it is enough to insert the elec­trodes into the body. ​“One of the most pop­u­lar exper­i­ments in elec­tro­chem­istry is to make a bat­tery by stick­ing appro­pri­ately selec­ted elec­trodes into a potato. We are doing some­thing sim­il­ar, the dif­fer­ence is that we are focus­ing on bio­fuel cells and the improve­ment of the cath­ode. And, of course, to have the whole pro­ject work­ing, we’d rather replace the potato with… a human being,” says Dr Mar­tin Jöns­son-Niedz­iółka (IPC PAS). In the exper­i­ments, Dr Jöns­son-Niedz­iółka’s group uses zinc-oxy­gen bat­ter­ies. The prin­ciple of their oper­a­tion is not new. The bat­ter­ies con­struc­ted in this way had been pop­u­lar before the time of alkaline power sources came. ​“At present, many labor­at­or­ies work on gluc­ose-oxy­gen bio­fuel cells. In the best case they gen­er­ate a voltage of 0.6−0.7 V. A zinc-oxy­gen biobat­tery with our cath­ode is able to gen­er­ate 1.75 V for many hours.,” says Adri­anna Złoczewska, a PhD stu­dent at the IPC PAS, whose research has been sup­por­ted under the Inter­na­tion­al PhD Pro­jects Pro­gramme of the Found­a­tion for Pol­ish Sci­ence. The main com­pon­ent of the biocath­ode developed at the IPC PAS is an enzyme sur­roun­ded by car­bon nan­otubes and encap­su­lated in a por­ous struc­ture — a silic­ate mat­rix depos­ited on an oxy­gen per­meable mem­brane. ​“Our group had been work­ing for many years on tech­niques that were neces­sary to con­struct the cath­ode using enzymes, car­bon nan­otubes and silic­ate matrices,” stresses Prof. Mar­cin Opałło (IPC PAS). An elec­trode so con­struc­ted is installed in a wall of a small con­tain­er. To have the bio­fuel cell work­ing, it is enough to pour an elec­tro­lyte (here: a solu­tion con­tain­ing hydro­gen ions) and insert the zinc elec­trode in the elec­tro­lyte. The pores in the silic­ate mat­rix enable oxy­gen sup­ply from the air and H+ ions from the solu­tion to act­ive centres of the enzyme, where oxy­gen reduc­tion takes place. Car­bon nan­otubes facil­it­ate trans­port of elec­trons from the sur­face of the semi­per­meable mem­brane. A cell with the new biocath­ode is able to sup­ply power with a voltage of 1.6 V, for a min­im­um one and a half of a week. The cell effi­ciency decreases with time, likely because of gradu­al deac­tiv­a­tion of the enzyme on the biocath­ode. ​“Here not everything is depend­ent on us, but on the pro­gress in bio­tech­no­logy. The life­time of a bio­fuel cells with our biocath­ode could be sig­ni­fic­antly pro­longed, if the enzyme regen­er­a­tion pro­cesses are suc­cess­fully developed,” says Dr Jöns­son-Niedz­iółka. In the exper­i­ments car­ried out so far, a stack of four bat­ter­ies con­nec­ted in series suc­cess­fully powered a lamp com­posed of two LEDs. Before, how­ever, the bio­fuel cells based on the design developed at the IPC PAS get pop­ular­ised, the research­ers must solve the prob­lem of rel­at­ively low elec­tric power that is com­mon to all types of bio­fuel cells. The research presen­ted here is import­ant not only in view of the mini­atur­isa­tion of power sup­ply sources for med­ic­al implants, bio­sensors or light-emit­ting tat­toos. The pro­cesses respons­ible for elec­tri­city gen­er­a­tion in bio­fuel cells are poten­tially suit­able for use in elec­tric power gen­er­a­tion in a lar­ger scale. The lim­it­ing factors here are the prop­er­ties of the enzymes, so that fur­ther advance­ment in this area is essen­tially depend­ent on the devel­op­ment of the bio­tech­no­logy. Source: Insti­tute of Phys­ic­al Chem­istry of the Pol­ish Academy of Sciences