Document:

<PAGE>

                                                                   Exhibit 10.43

September 19, 2000

Gregory A. Silvestri
15 Cinnamon Lane
Clifton Park, New York 12065

Re:  Employment Agreement

Dear Greg:

This letter will serve as an amendment to the existing employment arrangement
between you and Plug Power, Inc. ("Plug"), the terms of which are set forth in a
prior letter agreement dated June 1, 1999 as amended by subsequent letter
amendment dated August 3, 1999.  This second amendment to your employment
agreement shall be effective as of the date of your countersignature to this
letter, except as noted below.  The amended terms are as follows:

1.  Effective October 1, 2000, your base salary will be adjusted to an annual
rate of $225,000.  The base salary shall be earned and paid weekly.

2.  You will be paid a promotion bonus in the amount of $60,000 (gross) in
consideration of your August 24, 2000 promotion to Chief Operating Officer,
which such amount shall be payable within five (5) days of the effective date of
execution of this second letter amendment.

3.  You will be eligible for a target incentive bonus on the same terms and
conditions as currently set forth in the June 1, 1999 letter agreement.

4.  In the event of a termination of your employment for any reason, including
voluntary termination, you will be entitled to a full twelve (12) months salary
continuation at the full adjusted annual rate set forth in paragraph 1 above and
a full continuation of all of your current employee benefits for the same
period.  The continuation period shall commence as of the date of termination.
Additionally, your stock options will continue to vest, in accordance with the
governing stock option plan, for a twelve (12) month period following the
termination date, as if you continued to be an employee of Plug.

5.  The terms and conditions of this letter agreement shall survive both or
either of (a) the merger, reorganization or consolidation of Plug, or (b) the
sale of all or substantially all of the assets or stock of Plug.

Sincerely,

/s/ George C. McNamee

George C. McNamee
Chairman of the Board of Directors

The foregoing is agreed to and accepted by:

/s/ Gregory A. Silvestri          October 2, 2000
------------------------          ---------------
Gregory A. Silvestri                   Date<PAGE>

                                                                   Exhibit 10.44

                             DEVELOPMENT AGREEMENT
                             ---------------------

     This Agreement is made and entered into this second day of June, 2000,
("Effective Date") by and between Plug Power Inc., a Delaware corporation,
having a place of business at 968 Albany Shaker Road, Latham, New York 12110
(hereinafter referred to as "Plug"), and Engelhard Corporation, a Delaware
corporation, having a place of business at 101 Wood Avenue, Iselin, New Jersey
08830-0770 (hereinafter referred to as "Engelhard").

1.   Recitals
     --------

     1.1  Plug has developed and continues to develop technology and
manufacturing expertise related to fuel cell systems. Plug has developed and
continues to develop technology related to catalyst products useful in the
various components of fuel cell systems including fuel processors and fuel cell
stacks.

     1.2  Engelhard has developed and continues to develop technology related to
catalyst and sorbent, methods of manufacture and methods of application of
catalyst and sorbent compositions to substrates, including catalysts and
sorbents useful in the various components of fuel cell systems including fuel
processors and fuel cell stacks. Engelhard has also developed and continues to
develop technology related to the use of such catalysts and sorbents in fuel
cell systems useful in stationary and mobile applications.

     1.3  Plug and Engelhard desire to work together to design and develop
catalysts for use in Plug's fuel processors intended for use in Plug's
stationary fuel cell systems having a capacity to generate up to one hundred
(100) kW of electricity.

     In consideration of the foregoing and the terms set forth below, the
Parties agree as follows:
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2.   Definitions
     -----------

     The following terms shall have, for the purposes of this Agreement, the
meanings set forth in this Article 2. The terms may be used in this Agreement in
the plural or the singular form.

     2.1  "Materials" shall mean catalysts, sorbents, catalytic sorbents, and/or
reactive compounds and compositions which are useful in Fuel Processors to
catalyze the oxidation and/or reduction of, or otherwise treat components such
as, carbon monoxide, hydrogen, and hydrocarbons including components of natural
gas and LPG. Materials shall also include non-catalytic adsorbent materials
and/or absorbent materials useful in Fuel Processors.  Materials additionally
include catalyst materials supported on carriers such as honeycomb monoliths,
plates, pipes, hardware and Fuel Processors.  Specific Materials include, but
are not limited to, CO preferential oxidation catalysts and autothermal
reforming catalysts, oxidation catalysts for the abatement of hydrogen from the
anode of a fuel cell stack, and shift catalysts which are catalysts that
catalyze a gas stream comprising hydrogen, carbon monoxide and water to increase
the hydrogen concentration and decrease the carbon monoxide concentration of the
gas stream. Materials shall also include methods for application (e.g. coating)
of Materials onto substrates, and methods of use of these Materials.

     2.2  "Fuel Processor" shall mean a system (a) for converting hydrocarbon
fuels (e.g., natural gas, LPG etc.) to a gas containing hydrogen that is
suitable for acceptable operation at a fuel cell
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anode, and (b)intended for use in Plug's fuel cell systems designed for
stationary applications, including residential and small commercial
applications, and having a capacity to generate up to one hundred (100) kW of
electricity. The Fuel Processor may consist of hardware and control components
designed to employ Materials in reactor, exchanger, shift, CO polishing or
treatment subsystems

     2.3 "Program" shall mean the joint effort of the Parties pursuant to this
Agreement to design and develop Materials for use in Plug's Fuel Processors.

     2.4 "Project(s)" shall mean those projects relating to the Program which
are decided upon from time to time within the scope of the work outlined in
Exhibit A, made a part hereof, and as may be modified by the Parties in writing,
by mutual agreement from time to time.

     2.5 "Intellectual Property" shall mean any invention, discovery, concept,
expression or work, whether or not patented or patentable, including, without
limitation, discoveries, compositions, know-how, procedures, technical
information, processes, methods, test results, devices, formulas, protocols,
techniques, designs and drawings, any physical embodiment thereof, and any
patent (and applications therefor), copyrights (and applications therefor),
trade secret or other intellectual property right related thereto.

     2.6 "Affiliated Company" shall mean any company or entity owned by, or
having common ownership with either party to this Agreement, or being a joint
venture partner of either Party to this Agreement.

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Ownership of a company or entity as used herein means the direct or indirect
ownership of more than thirty percent (30%) of the voting shares or share
capital, equity or voting rights of the company or entity except that Affiliate
shall include Engelhard's affiliates N.E. ChemCat Co., Ltd. of Japan and Heesung
Engelhard of South Korea.
     2.7  "Product Specification" shall have the meaning set forth in the Supply
Agreement Section 1.6.

3.   Program for Establishment and Determination of Projects and Exchange of
     -----------------------------------------------------------------------
     Technical Information
     ---------------------

     3.1  Pursuant to the Program, Plug and Engelhard will cooperate in the
development of Materials for use in Plug's Fuel Processors in accordance with
the Project set forth in Exhibit A.  Generally, the goals of the Program shall
be to develop improved Materials that optimize the cost, performance and
durability of the Fuel Processor. Exhibit A will contain milestones which are
recognized by the Parties to be objectives and not obligations.  The Parties
further recognize that the milestones may change, as the Project progresses for
reason not anticipated. Therefore, the Parties agree that failure to meet a
milestone recited in Exhibit A shall not be a breach of this Agreement.

     3.2  Each Party shall appoint a representative as its project manager for
the Project (each such representative a "Project Manager").  The Project
                                         ---------------
Managers shall appoint members to their respective teams to work on the Project
and shall share overall responsibility for the coordination of the development
of the Product. Each Party's Project Manager shall be the other Party's point of

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contact for the resolution of any problems that may arise in connection with
this Agreement or the Project.  Each Party shall notify the other Party within
thirty (30) days after the execution of this Agreement of the appointment of its
Project Manager and shall notify the other Party as soon as practicable upon
changing such appointment.
     3.3  Exhibit A of this Agreement has been prepared by the business and
technical personnel of Engelhard and Plug who have met prior to the Effective
Date to outline the initial Project or Projects, within the scope of the
Program, to be undertaken. Such Project(s) shall include the nature, scope,
estimated resource requirements, milestones, performance and the estimated
completion date.

     3.4  The Parties shall meet as mutually agreed but at least every three (3)
months during the term of this Agreement.  During such meetings, each Party
shall review the status of the Projects, including:

          3.4.1  A review of current Projects, including reports of work done
subsequent to the previous meeting;

          3.4.2  The extent to which any previous or current Project is
proceeding towards commercialization; and

          3.4.3  A review of invention disclosures, patent applications filed or
issued relating to the Project, including contemplated foreign filings.
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          3.4.4  During the course of such meetings, the Parties shall decide
whether the Projects shall be modified and, if so, the Parties shall agree in
writing on specific actions to be taken by each Party.

          3.4.5  Minutes shall be taken at each meeting by each Party's Project
Leader or his/her designee and a written version of such minutes shall be
provided to the other Party within thirty (30) days of the conclusion of each
such meeting.
     3.5  Plug shall bear its own costs and expenses with respect to the
Program, and Engelhard shall be compensated for its costs and expenses with
respect to the Program in accordance with Article 4 hereinbelow. To the extent
Engelhard purchases property in accordance with, and for the primary purpose of
carrying out, the Project, any and all such property including materials,
equipment, software, and the like purchased or otherwise acquired by Engelhard
in connection with the Program, shall be the property of Engelhard, regardless
of whether the funds for such purchased or otherwise acquired property were
obtained using the compensation provided by Plug or by Engelhard.

     3.6  To the extent that either Party is prevented from disclosing
commercial and technical information hereunder by reason of obligations to third
parties, it shall use all reasonable efforts to secure the approval of such
third parties for the purpose of making disclosures hereunder.

4.   Engelhard Compensation

     4.1  Payment for Development Efforts Plug shall pay one hundred percent
          -------------------------------
(100%) of its own development costs and expenses incurred in
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connection with the Project. The Parties hereto agree that Ten Million Dollars
($10,000,000) represents the development costs and expenses estimated by
Engelhard and Plug that Engelhard will incur in connection with the Program from
the Effective Date through the third anniversary of the Effective Date. Plug
agrees to pay such development costs incurred by Engelhard in connection with
the Project (the "Development Fee"). The Development Fee shall be paid to
                  ---------------
Engelhard in cash in three installments as follows: Five Million Dollars
($5,000,000) within five (5) days of the Effective Date; Three Million Dollars
($3,000,000) within five (5) days of the first anniversary of the Effective
Date; and Two Million Dollars ($2,000,000) within five (5) days of the second
anniversary of the Effective Date.

     4.2 Investment in Plug:
         --------------------

     (a)  Within ten (10) days of the Effective Date, Plug shall issue and sell
to Engelhard, and Engelhard shall purchase from Plug, for a purchase price of
Five Million Dollars ($5,000,000) in cash such number of shares (the "Shares"),
Plug's common stock, par value one cent ($.01) per share (the "Common Stock")
having a market value of Five Million Dollars ($5,000,000) based on the
Effective Date Market Price (as defined below).  As used herein, "Effective Date
Market Price" means with respect to one share of Common Stock, the closing price
for such share ("Closing Price") as reported on NASDAQ for the trading day
immediately preceding the Effective Date; provided that in calculating such
Effective Date Market Price the Closing Price shall be reduced by five percent
(5%) of its arithmetic value.
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     (b) Within ten (10) days of the first anniversary of the Effective Date,
Plug shall issue and sell to Engelhard, and Engelhard shall purchase from Plug,
for a purchase price of Three Million ($3,000,000) in cash such number of Shares
of Common Stock having a market value of Three Million ($3,000,000) based on the
First Anniversary Market Price (as defined below).  As use herein First
Anniversary Market Price" means with respect to one share  of Common Stock, the
Closing Price as reported on NASDAQ for the trading day immediately preceding
the first anniversary of the Effective Date; provided that in calculating such
First Anniversary Market Price the Closing Price shall be reduced by five
percent (5%) of its arithmetic value.

     (c) Within ten (10) days of the second anniversary of the Effective Date,
Plug shall issue and sell to Engelhard, and Engelhard shall purchase from Plug,
for a purchase price of Two Million ($2,000,000) in cash such number of Shares
of Common Stock having a market value of Two Million ($2,000,000) based on the
Second Anniversary Market Price (as defined below).  As use herein, "Second
Anniversary Market Price" means with respect to one share  of Common Stock, the
Closing Price as reported on NASDAQ for the trading day immediately preceding
the second anniversary of the Effective Date; provided that in calculating such
Second Anniversary Market Price the Closing Price shall be reduced by five
percent (5%) of its arithmetic value.

     (d) Each obligation of Engelhard to purchase Common Stock pursuant to
clauses (a), (b) and (c) above is conditioned upon the
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receipt by Engelhard of the related installment payment of the Development Fee
as specified in Section 4.1.

     4.3 Engelhard hereby covenants that it shall use the entire Development Fee
primarily for its development activity in connection with the Project. Provided
that property purchased with the development fee can be used outside of the
Program.

5.   Intellectual Property
     ---------------------

     5.1  Ownership of Intellectual Property in the possession of either Party
prior to the date of this Agreement or developed outside the scope of this
Agreement, as substantiated by reasonable documentary evidence ("Background
                                                                 ----------
Intellectual Property"), shall be unaffected by this Agreement or the actions of
---------------------
the Parties pursuant to this Agreement.  Plug shall own all Plug Background
Intellectual Property and Engelhard shall own all Engelhard Background
Intellectual Property.

     5.2  All Intellectual Property developed hereunder: (a) solely by
Engelhard, (b) jointly by Engelhard and Plug, (c) or solely by Plug which relate
to Materials shall be the sole property of Engelhard ("Engelhard Intellectual
Property").

     5.3  Except as recited in Section 5.2, all Intellectual Property developed
hereunder: (a) solely by Plug, (b) jointly by Plug and Engelhard, or (c) solely
by Engelhard which relate to the Fuel Processors shall be the sole property of
Plug ("Plug Intellectual Property").
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     5.4  Each party having sole property rights in Sections 5.2 and 5.3
respectively, shall, at its sole discretion, file patent applications in the
United States of America and foreign countries covering such property rights.
Where Confidential Information developed hereunder of a non-filing Party is
required to file a patent application, the filing Party shall request permission
of the non-filing Party to use such Confidential Information, and the non-filing
Party shall not unreasonably withhold such permission.

     5.5  Except as otherwise provided, and in order to carry out the
foregoing, each Party shall, at the request of the other Party, use reasonable
efforts to execute or cause to be executed such assignments or other papers
relating to Intellectual Property rights, including the assignment of patent
applications, as the requesting Party may require.  Each Party agrees that its
employees shall cooperate with and assist the other Party (at no cost to the
other Party) in the preparation and prosecution of other Party's patent
applications.
     5.6  During the term of this Agreement and the term of the Supply
Agreement, whichever is longer, Engelhard shall not provide to any third party
the Product Specification or Materials, when taken in the aggregate, meet the
Product Specification, except: (i) in compliance with Section 6.3; (ii) or if
Engelhard is acquired by another entity or merges with another entity, the
Product Specification can be disclosed to such acquiring or merging entity;
(iii) or the part of Engelhard's business to which the Product Specification is
sold or otherwise divested from Engelhard, the Product Specification can be
provided to the divesting part of the business; provided that the divested part
of the business agrees to be bound by the terms and conditions of this Agreement
and the Supply Agreement; or (iv) or if
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the Product Specification falls within Engelhard's Background Intellectual
Property as defined in Section 5.1.

     Notwithstanding the foregoing, and notwithstanding any other provision in
this Agreement or in the Supply Agreement, Engelhard may (without disclosing
Plug's use of any particular product or specification) provide any product to be
sold by Engelhard to Plug or any Product Specification, to any third party for
applications outside the field of Fuel Processors.

6.   Confidential Information
     ------------------------

     6.1  Plug and Engelhard recognize that in order to carry out the intent of
this Agreement, the exchange of certain commercial and technical information
will be required and that such commercial and technical information may
constitute proprietary information of the Party furnishing the same
("Confidential Information"). Each of the Parties hereto agrees that all
Confidential Information related to the Program and furnished to it by the other
Party in writing shall be marked as proprietary or confidential.  Confidential
Information disclosed by oral or visual means shall be designated at the time of
the original disclosure as being proprietary or confidential and thereafter
reduced to written form, marked confidential and delivered to the receiving
Party within twenty (20) days of the original. Confidential Information which
shall not be considered proprietary or confidential hereunder includes
information:

     (a)  that is or becomes publicly available other than through the fault or
          negligence of the receiving Party;
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     (b)  that is rightly obtained without restriction by the receiving Party
          from a third party;
     (c)  that was known by the receiving Party or the public prior to its
          receipt; or
     (d)  that is released without restriction by the providing Party to anyone;
          or
     (e)  that is developed by the receiving Party independently of the
          providing Party and without breach of this Agreement, and such
          independent development is demonstrated by the receiving Party with
          acceptable relevant documentary evidence.
Each Party hereto agrees that it shall not use Confidential Information of the
other except in performance of this Agreement, or disclose the same to third
parties, without the prior written approval of the other Party. Each Party shall
advise its employees having access to Confidential Information of the Party's
obligations hereunder and will disclose such Confidential Information only to
those of its employees who are subject to written obligations restricting use
and disclosure of such information to at least the same extent as provided in
this Agreement. The confidentiality obligations of the Parties hereunder shall
cease seven (7) years from the date of termination of this Agreement.

     6.2  With regard to samples (including, but not limited to Materials, Fuel
Processors and/or any components thereof collectively and fuel cell stacks
and/or components thereof, collectively, the "Samples") and received, directly
or indirectly, by one Party from the other, the receiving Party agrees as
follows:
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     (i)   not to analyze or have analyzed any of the Samples in order to
determine the physical or structural characteristics or chemical composition of
any of the Samples;
     (ii)  not to provide the Samples to third parties;
     (iii) to use the Samples only for the Project;
     (iv)  upon completion of receiving party's evaluation and unless otherwise
agreed, the receiving Party shall return all used and unused Samples to the
disclosing Party; and
     (v)   to provide each other with the results of each Party's evaluation of
other Party's Samples and otherwise hold such Samples and results as
Confidential Information subject to this Article 6.

     6.3  In the event that a Party is required to disclose Confidential
Information or Samples or results which a Party is obligated to maintain in
confidence under this Agreement to a third party in response to a subpoena or
order of a court or administrative agency, the Party required to disclose shall
inform the other Party promptly so that the other Party shall have the
opportunity to seek a protective order or to limit the scope of the requested
disclosure and, provided, that Party required to disclose shall not interfere
with the other Party's lawful efforts to obtain said protective order.

     6.4  Each Party will have sole discretion to determine what Confidential
     Information or Background Intellectual Property it is required to disclose
     to the other Party hereunder. Neither Party shall be required to disclose
     to the other, or any third party, Sample compositions or methods of
     application whether part of Background Intellectual Property or
     Intellectual Property developed under this Agreement.

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7.  Shares of Plug Power Stock
    --------------------------

     7.1  Valid Issuance of Shares.  Plug represents and warrants that when
          -------------------------
issued and delivered in accordance with the terms hereof, the Shares will be
duly authorized and validly issued.  Subject to Engelhard's compliance with
Section 7.2, the Shares will be issued in compliance with all applicable federal
securities laws.

     7.2  Accredited Investor Representations and Warranties.  In connection
          --------------------------------------------------
with acquiring the Shares, Engelhard hereby represents and warrants to Plug that
Engelhard is an "accredited investor," within the meaning of Rule 501 of
Regulation D under the Securities Act.

     7.3  Transfer Restrictions.  Engelhard shall not, directly or indirectly,
          ---------------------
sell, transfer, assign, pledge or otherwise dispose of any interest in any of
the Shares acquired hereunder for a period of three (3) years following the
acquisition of such Shares (the "Holding Period"); provided that such agreement
shall not be deemed to limit Engelhard's right to surrender its Shares in a
merger or other corporate transaction involving a change of control of Plug as a
result of which Shares may be deemed to be transferred by operation of law to a
successor in interest of Plug; and provided further that, notwithstanding
anything in this Section 7.3 to the contrary, Engelhard shall be permitted to
(i) sell, transfer, assign or pledge all or any part of the Shares to (A) any
direct or indirect subsidiary of Engelhard or (B) any Affiliated Company of
Engelhard.
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     7.4  Legends.  It is understood that each certificate evidencing Shares
          -------
          will bear the following legend:

     THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN REGISTERED
     UNDER THE SECURITIES ACT OF 1933, AS AMENDED, HAVE BEEN ACQUIRED FOR THE
     HOLDER'S OWN ACCOUNT AND HAVE BEEN ACQUIRED FOR INVESTMENT AND NOT WITH A
     VIEW TO, OR IN CONNECTION WITH, THE SALE OR DISTRIBUTION THEREOF.  NO
     OFFER, SALE OR DISPOSITION OF THESE SECURITIES MAY BE EFFECTED WITHOUT AN
     EFFECTIVE REGISTRATION STATEMENT RELATED THERETO OR AN OPINION OF COUNSEL
     FOR THE COMPANY THAT SUCH REGISTRATION IS NOT REQUIRED UNDER THE SECURITIES
     ACT OF 1933.  IN ADDITION, THE HOLDER OF THE SECURITIES REPRESENTED BY THIS
     CERTIFICATE HAS AGREED NOT TO DIRECTLY OR INDIRECTLY SELL, TRANSFER,
     ASSIGN, PLEDGE OR OTHERWISE DISPOSE OF ANY SUCH SHARES OTHER THAN IN
     ACCORDANCE WITH AN AGREEMENT DATED AS OF JUNE 2, 2000 WITH THE COMPANY, A
     COPY OF WHICH IS ON FILE WITH THE COMPANY.

     Notwithstanding the foregoing, Engelhard shall have the right, upon written
request to Plug on or after termination of all applicable limitations on
transfer with respect to any Shares, to receive from Plug, without expense, a
new certificate omitting any legend with respect to the terminated limitations.

     7.5  SEC Reports and Financial Statements.  In connection with the
          -------------------------------------
issuance of the Shares, Plug hereby represents and warrants, as of the date
hereof and as of each date on which Shares are issued, that: (i) it has filed or
will have been filed with the Securities and Exchange Commission (the "SEC") all
forms, reports, schedules,
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statements and other documents required to be filed by it since October 28, 1999
under the Securities Exchange Act of 1934, as amended (the "Exchange Act") or
the Securities Act of 1933, as amended (the "Securities Act") (as such documents
have been amended since the time of their filing, collectively, the "SEC
Documents"); (ii) The SEC Documents, including without limitation any financial
statements and schedules included therein, at the time filed (a) did not contain
any untrue statement of a material fact or omit to state a fact, which is
material, required to be stated therein or necessary in order to make the
statements therein, in light of the circumstances under which they were made,
not misleading and (b) complied in all material respects with the applicable
requirements of the Exchange Act and the Securities Act, as the case may be, and
the applicable rules and regulations of the SEC thereunder; and (iii) the
financial statements of Plug included in the SEC Documents comply as to form in
all material respects with applicable accounting requirements and with the
published rules and regulations of the SEC with respect thereto, have been
prepared in accordance with generally accepted accounting principles applied on
a consistent basis during the period involved (except as may be indicated in the
notes thereto or, in the case of the unaudited statements, as permitted by Form
10-Q of the SEC) and fairly present (subject, in the case of the unaudited
statements, to normal, recurring audit adjustments) the consolidated financial
position of Plug and its consolidated subsidiaries as at the dates thereof and
the consolidated results of their operations and cash flows for the periods then
ended.

8.  Commercial Arrangements
    -----------------------
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          Concurrent with the Effective Date, the Parties have executed a Supply
Agreement in the form attached hereto as Exhibit B.

9.   Publicity
     ---------

     No public release or advertisements by either Plug or Engelhard relating to
the subject of this Agreement shall be made without the prior written agreement
of both Parties except to the extent that either Party is advised by its counsel
that disclosure of such subject is required by law; provided that in the event
that a Party has been so advised by counsel, the other Party will be afforded
the opportunity to review such press release prior to its public dissemination.

10.  Warranties and Limitation of Liabilities
     ----------------------------------------

     10.1  No Party shall be liable to the other Party under this Agreement
except for liability associated with Articles 4, 5, 6, 7 and 9.

     10.2  The sole obligation of each Party with respect to its commercial and
technical information, including the results of the Projects of Section 3.4,
shall be to provide same to the other Party as provided in this Agreement, and
to correct errors that might have occurred in said information without undue
delay after such errors are made known to the Party which forwarded said
information.

     10.3  Nothing in this Agreement shall obligate either Party to apply for,
maintain or acquire any patent protection, in any country.
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11.  Notices
     -------

     All notices required to be given hereunder shall be in writing and shall be
given by first class mail, postage prepaid, addressed to the Parties as follows:

     To Plug:       Plug Power Inc.
                    968 Albany Shaker Road
                    Latham, New York 12110
                    Attn: Gary Mittleman
                          President & CEO

                    cc:  General Counsel

     To Engelhard:  Engelhard Corporation
                    101 Wood Avenue South
                    Iselin, NJ  08830-0770

                    Attn:    Daniel W. Parker
                             Group Vice President
                             and General Manager
                             Separation Systems & Ventures

                    cc:      Vice President & General Counsel

Either Party shall have the right to change the address to which notices are to
be sent by the giving of not less than ten (10) days written notice to the other
Party.

12.  Relationship
     ------------

     The relationship of the Parties hereto shall be that of independent
contractors and nothing herein contained shall be deemed to create any
relationship of agency.
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13.  Entire Agreement
     ----------------

     This Agreement constitutes the entire agreement between the Parties
regarding the joint development of the Materials specified in Exhibit A hereto
and supersedes any and all other prior agreements and understandings whether
written, verbal or implied. No changes, alterations or modifications to this
Agreement shall be effective unless in writing and signed by the Parties hereto.

14.  Termination
     -----------

     This Agreement shall terminate the later of (i) three (3) years from the
Effective Date or (ii) the date on which Engelhard has exhausted the Development
Fee, unless further extended by written agreement of the Parties. Upon
termination pursuant to this Section 14, the Parties shall be relieved of all
obligations under this Agreement, except for their obligations under Sections 4
through 8 and this Section 14.

     In no event shall termination of this Agreement have any bearing on the
effect or survivability of the Supply Agreement.

15.  Other Development
     -----------------

     Either Party hereto, subject to its obligations under Section 6 above in
connection with the other Party's Confidential Information, may pursue
development activity, whether or not similar to the
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Program, with others or independently, provided such activity does not otherwise
violate a Party's obligations hereunder. Engelhard hereby gives notice to Plug
that it has a variety of relationships with other Fuel Cell System manufacturers
and development companies.
16.  Governing Law
     -------------

     This Agreement shall be governed by and construed in accordance with the
laws of the State of New Jersey without giving effect to principles of conflicts
of laws that would cause the application of the laws of any jurisdiction other
than the State of New Jersey.

17.  Authority/No Conflicts
     ----------------------

     Each Party represents and warrants that (i) it has full power and authority
and legal right to execute and deliver this Agreement, (ii) its execution,
delivery and performance of this Agreement have been duly authorized by all
necessary action, (iii) this Agreement has been duly executed and delivered by
it and (iv) this Agreement constitutes its legal, valid and binding obligation,
enforceable in accordance with its terms, except that such enforceability may be
limited by applicable bankruptcy, insolvency, reorganization, moratorium or
similar laws affecting the rights of creditors generally and by the availability
of the remedy of specific performance.

18.  Waiver, Discharge, etc.
     ----------------------

     This Agreement may not be released, discharged, abandoned, changed or
modified in any manner, except by an instrument in writing signed on behalf of
each of the Parties by their duly authorized
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Page 21

representatives. The failure of either Party to enforce at any time any of the
provisions of this Agreement shall in no way be construed to be a waiver of any
such provision, nor in any way to affect the validity of this Agreement or any
part of it or the right of either Party after any such failure to enforce each
and every such provision. No waiver of any breach of this Agreement shall be
held to be a waiver of any other or subsequent breach.

19.  Counterparts
     ------------

     This Agreement may be executed in one or more counterparts, all of which
shall be considered one and the same agreement, and shall become a binding
agreement when one or more counterparts have been signed by each Party and
delivered to the other Party.

20.  Captions, Construction
     ----------------------

     The titles and headings to Sections herein are inserted for the convenience
of reference only and are not intended to be a part of or to affect the meaning
or interpretation of this Agreement.  This Agreement shall be construed without
regard to any presumption or other rule requiring construction hereof against
the Party causing this Agreement to be drafted.

21.  No Third Party Benefits
     -----------------------

     Nothing in this Agreement, expressed or implied, is intended to confer on
any person other than the Parties or their respective
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Page 22

permitted successors or assigns, any rights, remedies, obligations or
liabilities under or by reason of this Agreement.

22.  No Implied Licenses
     -------------------

     No rights or licenses with respect to a Party's Intellectual Property,
Confidential Information or other proprietary rights are granted or deemed
granted to the other Party hereunder or in connection herewith, other than those
rights expressly granted in this Agreement.

23.  Assignment
     ----------

     Neither Party shall have the right to transfer or assign its interest in
this Agreement or delegate its obligations under this Agreement without the
prior written consent of the other Party.

     IN WITNESS WHEREOF, the Parties hereto have caused this Agreement to be
executed as of the day and year first above written.

PLUG POWER INC.                    ENGELHARD CORPORATION

     /s/ Gary Mittleman                   /s/ Daniel W. Parker
By: ___________________________    By: ____________________________
     Gary Mittleman                       Daniel W. Parker
     President & CEO                      Group Vice President
                                          and General Manager

         June 6, 2000                         June 2, 2000
Date: _________________________    Date: __________________________

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