Green En­ergy Break­through: Hy­dro­gen Har­vest­ing With Sea­wa­ter Elec­trol­y­sis

Trillions - - In This Issue -

An in­ter­view with Daniel Es­pos­ito, As­sis­tant Pro­fes­sor of Chem­i­cal En­gi­neer­ing at Columbia Uni­ver­sity.

Hy­dro­gen is one of the many promis­ing clean fuel sources of the fu­ture. Un­for­tu­nately, the dom­i­nant ap­proaches used to date to pro­duce it in a suf­fi­cient vol­ume in­volve the use of meth­ane, it­self a green­house gas, in a re­ac­tion that also re­leases car­bon diox­ide (CO ).

2 Daniel Es­pos­ito, an as­sis­tant pro­fes­sor at Columbia Uni­ver­sity’s Chem­i­cal En­gi­neer­ing de­part­ment, is work­ing with a team to in­vent a very dif­fer­ent way of pro­duc­ing clean en­ergy: ef­fi­ciently and with no harm­ful emis­sions.

The technology they are cre­at­ing is what ap­pears to be a so­lu­tion that al­lows the pro­duc­tion of hy­dro­gen us­ing mem­brane-free elec­trol­y­sis, it­self a first-of-it­skind in­no­va­tion, en­vi­sioned to be used on a rig that would float on sea­wa­ter and it­self be pow­ered solely by so­lar en­ergy. If and when the technology be­comes a mass-man­u­fac­turable re­al­ity, it could change the world of clean en­ergy for bil­lions around the globe.

Tril­lions spoke to Dr. Es­pos­ito in his of­fices at Columbia Uni­ver­sity.

Tril­lions: Could you de­scribe your role at Columbia and what you do there?

Daniel Es­pos­ito: I am in my fourth year as an as­sis­tant pro­fes­sor in the Chem­i­cal En­gi­neer­ing de­part­ment here at Columbia. As an as­sis­tant pro­fes­sor, my re­spon­si­bil­i­ties in­clude not only teach­ing classes but also run­ning a re­search lab.

The par­tic­u­lar lab that I run here is called the So­lar Fu­els En­gi­neer­ing Lab. The over­ar­ch­ing goal and ob­jec­tive of our re­search in this lab is to de­velop ma­te­ri­als and de­vices that will help more ef­fi­ciently con­vert so­lar en­ergy, or elec­tric­ity from so­lar pho­to­voltaics, into storable chem­i­cal fu­els.

Tril­lions: It is cer­tainly some­thing that will make a big dif­fer­ence. One of the things that a lot of read­ers out there prob­a­bly aren’t even aware of is how much hy­dro­gen is be­ing pushed glob­ally [as an al­ter­nate fuel]. Toy­ota is putting an en­tire ecosys­tem into place, over in Ja­pan, where even de­liv­ery trucks and [the means of] grab­bing your hy­dro­gen “on the go” are all be­ing set up as in­fra­struc­ture. With in­no­va­tions like what you’re talk­ing about, it should make it pos­si­ble to make use of this sooner than a lot of peo­ple re­al­ize.

What ex­actly is this in­no­va­tion that you’ve been work­ing on, on the na­ture of wa­ter elec­trol­y­sis us­ing so­lar en­ergy?

Daniel Es­pos­ito: The in­no­va­tion in what we’ve done, in this most re­cent study, is at two dif­fer­ent lev­els. At one level, the in­no­va­tion is a novel elec­trode ar­chi­tec­ture that al­lows us to split wa­ter into oxy­gen and hy­dro­gen with­out the pres­ence of a mem­brane or di­vider sep­a­rat­ing those two elec­trodes or a pump that’s used to flow the liq­uid elec­trolyte through the de­vice. With this ar­chi­tec­ture that we’ve de­vel­oped for these elec­trodes, it’s very sim­ple.

With that sim­plic­ity comes po­ten­tially low-cost man­u­fac­tur­ing and assem­bly of these de­vices. This is par­tic­u­larly im­por­tant in a re­new­able en­ergy fu­ture, be­cause the price of elec­tric­ity from re­new­able en­ergy gen­er­a­tors like so­lar and wind has dropped sub­stan­tially in re­cent years and will con­tinue to do so go­ing for­ward. So, when you look at the eco­nom­ics of these wa­ter elec­trol­y­sis sys­tems for pro­duc­ing hy­dro­gen, that puts a big em­pha­sis on de­creas­ing cap­i­tal costs in or­der to make hy­dro­gen pro­duc­tion com­pet­i­tive with con­ven­tional hy­dro­gen pro­duc­tion technology, which is steam meth­ane re­form­ing.

Steam meth­ane re­form­ing is a cheap process right now be­cause natural gas is very cheap. Of course, a down­side of steam meth­ane re­form­ing is that it also emits CO2 in the process. So, wa­ter elec­trol­y­sis driven by re­new­able re­sources is a car­bon-free method of pro­duc­ing a car­bon-free fuel.

That was in­no­va­tion num­ber one – the sim­plic­ity of the elec­trode ar­chi­tec­ture that’s used within these elec­trol­y­sis de­vices.

The sec­ond in­no­va­tion is more at the de­vice or sys­tem level, where we have im­ple­mented this mem­brane-free ar­chi­tec­ture into a big­ger sys­tem or de­vice that floats on the sur­face of the wa­ter. Hence the name we came up with, which is “so­lar fu­els rig.”

There are ex­am­ples of other peo­ple in lit­er­a­ture who have thought of do­ing some­thing along the lines of this.

But, to our knowl­edge, this is the first demon­stra­tion of a prac­ti­cal de­vice that in prin­ci­ple could be scaled up and op­er­ated to gen­er­ate large quan­ti­ties of CO2 - free hy­dro­gen.

Tril­lions: I have this image of see­ing … this … out­side. You see wind en­ergy now in ar­eas where that might have been a sur­prise. Or you see so­lar panel in­stal­la­tions … [in­clud­ing] a mas­sive one that went into West Vir­ginia re­cently over an old mine, which is a won­der­ful way of mak­ing use of it. They’re also do­ing a sim­i­lar thing in China with that. Here we have the idea that we might have the float­ing rigs [you’ve de­scribed] out there, so you’re ba­si­cally min­ing the wa­ter in a very dif­fer­ent way.

Let’s go into a lit­tle more de­tail into the technology, the na­ture of elec­trol­y­sis, how it works and how your ap­proach with mem­brane-less elec­trol­y­sis works in this par­tic­u­lar sit­u­a­tion.

Daniel Es­pos­ito: At a high level, let’s talk about what wa­ter elec­trol­y­sis is. An­other name for it is “wa­ter split­ting.” As is im­plied by that name, you need to put en­ergy into an elec­trolyzer sys­tem to split wa­ter into its two com­po­nents: oxy­gen and hy­dro­gen. Based on the sto­i­chiom­e­try of wa­ter, which is H2O, you get two times the amount of hy­dro­gen as you get oxy­gen.

This is a ther­mo­dy­namic up­hill re­ac­tion, mean­ing you need to put en­ergy into it to go from wa­ter to oxy­gen and hy­dro­gen. There are a num­ber of ways you can do that, but elec­trol­y­sis is one that we and many other peo­ple be­lieve is re­ally at­trac­tive for fa­cil­i­tat­ing this re­ac­tion. In elec­trol­y­sis, the in­put source of en­ergy to drive wa­ter split­ting is elec­tric­ity, and this is done through an elec­tro­chem­i­cal process. So, as is im­plied by that word “elec­tro­chem­i­cal,” you are con­vert­ing elec­tri­cal en­ergy into chem­i­cal en­ergy in the form of the chem­i­cal bond within the hy­dro­gen fuel that’s pro­duced.

In elec­tro­chem­i­cal wa­ter split­ting, one of­ten views the over­all elec­tro­chem­i­cal re­ac­tion as two sep­a­rate half re­ac­tions. The two half re­ac­tions that are rel­e­vant for wa­ter split­ting are the oxy­gen and hy­dro­gen evo­lu­tion re­ac­tions. The hy­dro­gen evo­lu­tion re­ac­tion oc­curs at the cath­ode, which is one of two elec­trodes within the elec­trolyzer. The oxy­gen evo­lu­tion re­ac­tion takes place at the an­ode, which is the other elec­trode within the elec­trolyzer.

Dur­ing elec­trolyzer op­er­a­tion, a first im­por­tant task is to pro­duce the oxy­gen and the hy­dro­gen by elec­trol­y­sis, and the sec­ond im­por­tant task is to en­sure that these two prod­uct species re­main sep­a­rate Photo by from Pe­dro each Lu­peron, other. CC Hy­dro­gen is re­ally, for the vast ma­jor­ity of ap­pli­ca­tions,

the valu­able fuel that we’re most in­ter­ested in. If you get this mix­ture of oxy­gen and hy­dro­gen, that’s go­ing to de­crease the value of the hy­dro­gen be­cause it will be less pure. Sec­ondly, it can cre­ate a safety hazard, be­cause a mix­ture of hy­dro­gen and oxy­gen can be highly flammable. So it’s re­ally im­por­tant dur­ing elec­trol­y­sis to make sure the oxy­gen and the hy­dro­gen that are be­ing pro­duced re­main sep­a­rate from each other.

In con­ven­tional elec­trolyz­ers, mem­branes or nanoporous or mi­cro­p­orous di­viders called di­aphragms are used to sep­a­rate the two elec­trodes. They still al­low ionic cur­rent to trans­fer be­tween the two elec­trodes, but they serve as phys­i­cal bar­ri­ers to block the oxy­gen and hy­dro­gen from cross­ing be­tween the gap that sep­a­rates the two elec­trodes.

In our re­search, a key in­no­va­tion that al­lowed us to avoid the use of these di­viders was re­lated to the struc­ture of the elec­trodes used within the de­vice. These elec­trodes are what are called “porous flowthrough elec­trodes.” They look just like the screen that you would find in a win­dow or a screen door that al­lows air through but keeps the bugs out. What we did was to take two pieces of mesh elec­trodes and de­posit a spe­cial metal­lic ma­te­rial, called the cat­a­lyst, on only the outer sur­faces of these two mesh elec­trodes. So, if you are look­ing at a side view of our con­fig­u­ra­tion, the two mesh screens are placed in a face-to-face con­fig­u­ra­tion and the metal cat­a­lyst, where the re­ac­tion takes place, is de­posited only on the outer sur­faces. The cat­a­lyst is where the re­ac­tion oc­curs, as I just men­tioned. So, be­cause it’s placed only on the outer sur­face, that’s where the gaseous oxy­gen and hy­dro­gen prod­ucts form.

As a gaseous prod­uct, these prod­ucts want to float up­wards within the aque­ous elec­trolyte from which they form. That buoy­ancy force causes those bub­bles to float up­wards into sep­a­rate col­lec­tion cham­bers be­fore the bub­bles have a chance to cross over be­tween the gap that sep­a­rates those two elec­trodes. We re­fer to this phe­nom­e­non as “buoy­ancy-in­duced sep­a­ra­tion” of the oxy­gen and hy­dro­gen prod­ucts.

Tril­lions: That’s very clever, in terms of how you’re sep­a­rat­ing the two gases in there. [You made] a very good point, that the hy­dro­gen, of course, is the fuel and the O2 is a won­der­ful place to burn things in, so you want to be care­ful about keep­ing the two of them sep­a­rated.

How far along is this, and what kind of ex­per­i­men­tal re­sults have you seen in ef­fi­ciency of op­er­a­tion or scal­a­bil­ity?

Daniel Es­pos­ito: Ev­ery­thing that we’ve done so far has in­volved lab-scale demon­stra­tions. The minia­ture so­lar fu­els rig that we demon­strated in our lab is about

eight inches or so across. So, the quan­tity of hy­dro­gen that’s pro­duced by this is very small. [It’s] maybe enough to power the elec­tron­ics for your phone, but to have a mean­ing­ful im­pact on global en­ergy use, this is some­thing that would have to be scaled up over acres, if you wanted to ser­vice the fuel needs of, say, a town. Sig­nif­i­cantly larger ar­eas would be needed if you wanted to ex­pand to the level of im­pact­ing state or na­tion­wide en­ergy use.

In prin­ci­ple, though, what we’ve done is re­ally promis­ing, be­cause the ba­sic de­sign should be scal­able with­out im­pact­ing the ef­fi­ciency or the prod­uct pu­rity. There are cer­tainly some ad­just­ments and some op­ti­miza­tion that we and oth­ers will need to do to get there, but I think they are largely solv­able en­gi­neer­ing prob­lems.

The other ques­tion be­hind this is the eco­nom­ics. How much is it go­ing to cost to con­struct these things, and will the price of the hy­dro­gen pro­duced with this technology be able to com­pete with hy­dro­gen pro­duced by the con­ven­tional steam meth­ane re­form­ing process? At this point, we re­ally don’t know, but we are very op­ti­mistic that the sim­plic­ity of our de­vices and like­li­hood of im­prov­ing their per­for­mance fur­ther will cre­ate op­por­tu­ni­ties to com­pete not only with con­ven­tional elec­trolyzer de­signs but also fos­sil fu­els.

Tril­lions: That’s a chal­lenge that, un­til you ac­tu­ally have be­gun to try scal­ing it up, as well as think about the lo­gis­tics of how you move what you’ve gath­ered to where it needs to get to, [you can’t be sure].

Daniel Es­pos­ito: So there needs to be a larger in­fra­struc­ture in place. Which is some­thing that some coun­tries – Ja­pan is one that you men­tioned – have made a lot of progress in these re­gards in re­cent years. It’s also prob­a­bly go­ing to be lo­ca­tion-de­pen­dent. It’s also go­ing to be help­ful if there’s al­ready an in­dus­try that’s con­sum­ing large amounts of hy­dro­gen. When hy­dro­gen is dis­cussed as a fuel, peo­ple gen­er­ally think of it as a car­bon-free “fuel of the fu­ture.” But the truth of the mat­ter is that, glob­ally, we con­sume mas­sive amounts of hy­dro­gen al­ready to­day, us­ing large amounts of en­ergy to pro­duce it. To be ex­act, we use about eight quads worth of en­ergy ev­ery year to pro­duce hy­dro­gen. A quad is [equal to] a quadrillion BTUS. Just as a ref­er­ence, the United States’ to­tal an­nual en­ergy use is 100 quads. So, we’re talk­ing about a big amount of en­ergy that’s al­ready used to pro­duce hy­dro­gen, and there’s a large as­so­ci­ated amount of hy­dro­gen with that. A lot of that goes to the chem­i­cal in­dus­try, for ex­am­ple, for mak­ing chem­i­cals like ammonia, which is re­ally im­por­tant for fer­til­iz­ers and feeds bil­lions of peo­ple on this planet. An­other im­por­tant chem­i­cal is methanol, which uses hy­dro­gen as a feed­stock.

So, if you can co-lo­cate these wa­ter elec­trol­y­sis fa­cil­i­ties close to where you have some of these large chem­i­cal plants that are us­ing hy­dro­gen from steam meth­ane re­form­ing, then that can have a big im­pact. And, in prin­ci­ple, the in­fra­struc­ture [to make use of the hy­dro­gen] is al­ready there to­day.

Hy­dro­gen can [also] be a uni­ver­sal CO2 -free fuel. Hy­dro­gen can be used not only as trans­porta­tion fuel but also as the fuel for space heat­ing and cook­ing. You can, us­ing fuel cells, con­vert hy­dro­gen back to elec­tric­ity. So, it’s help­ful for the elec­tri­cal util­ity [in­dus­try too]. When you have that in­fra­struc­ture in place, it ben­e­fits all these dif­fer­ent sec­tors.

Tril­lions: What’s next for the project? What are your plans and what do you hope to do?

Daniel Es­pos­ito: I think [there are] a lot of re­ally neat things to work on here, both at the level of the ma­te­rial that goes into the elec­trolyz­ers and then the en­gi­neer­ing that in­volves the de­sign and op­ti­miza­tion of the de­vices and the plat­forms them­selves. One par­tic­u­larly im­por­tant area mov­ing for­ward is to op­ti­mize and de­velop bet­ter cat­a­lysts that are coated on the outer sur­faces of those mesh elec­trodes, par­tic­u­larly for sea­wa­ter elec­trol­y­sis. A lot of the ex­per­i­ments that we’ve done up to this point have ac­tu­ally been done in acidic elec­trolyte, whereas, in con­trast, sea­wa­ter is rel­a­tively ph-neu­tral and con­tains a lot of chlo­ride ions. Chlo­ride ions are a con­cern for wa­ter elec­trol­y­sis be­cause (a) they can be fairly cor­ro­sive, and (b) chlo­ride ions can re­com­bine to form chlo­rine gas at the an­ode of elec­trol­y­sis cells. So that rep­re­sents a re­ac­tion, at the an­ode, that’s com­pet­ing with the oxy­gen evo­lu­tion re­ac­tion. Mov­ing for­ward, we would need to put more ef­forts into de­vel­op­ing cat­alytic ma­te­ri­als that will se­lec­tively pro­mote oxy­gen evo­lu­tion as op­posed to chlo­rine evo­lu­tion. Also, just in gen­eral, [it is im­por­tant to de­velop] cat­a­lysts for both elec­trodes that are ro­bust and sta­ble for op­er­a­tion in sea­wa­ter for long pe­ri­ods of time.

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